Forces

Question 1

Describe what is Meant by a Scalar Quantity

Answer 1

-Scalar quantities only have a magnitude. They do not have a direction.

Examples include:
-Distance, Speed, Temperature, Mass, Energy

Question 2

Describe what is Meant by a Vector Quantity

Answer 2

-Vector quantities have both a magnitude and a direction.

Examples include:
-Force, Velocity, Momentum, Acceleration, Displacement

-Vector quantities are usually shown by an arrow- the length of the arrow shows the magnitude, and the direction of the arrow shows the direction of the quantity.

Question 3

Describe how to Draw a Free Body Diagram

Answer 3

-Draw the arrow with a ruler to scale.

-Label the arrow with the quantity.

-Show the object with a dot on the end of the arrow.

-Positive quantities are shown to the right and negative quantities are shown to the left.

Question 4

Describe the Effects of Forces in Physics

Answer 4

-A force is a push or a pull experienced when one object interacts with another object.

-Forces can change the speed or direction that an object moves. Forces can also change an object’s shape.

-Because forces have magnitude (size) and direction, this means that forces are vector quantities. The unit of force is the newton (N).

-A contact force can take place when objects are touching. If the objects experience a force when they are not touching, then this is an example of a non-contact force.

Question 5

Describe the Features of the Main Non-Contact Forces

Answer 5

Gravitational Force is always an attractive force. It acts between all objects e.g. between a planet and a satellite.

Electrostatic force can attract or repel. It acts between objects that have a charge e.g. between two positive particles.

Magnetic force can attract or repel. It acts between magnets and certain objects e.g. between two magnetic north poles.

Question 6

Describe the Features of the Main Contact Forces

Answer 6

-An object at rest on a surface experiences reaction force.

-An object that is being stretched experiences a tension force.

-Two objects sliding past each other experience friction forces.

-An object moving through the air experiences air resistance.

Question 7

Describe what is Meant by Gravitational Force

Answer 7

-Gravity attracts all masses. All objects with mass produce a gravitational field.

-On the surface of a planet, gravity causes all things to fall to the ground. It also gives everything a weight.

Question 8

Describe the Difference Between Weight and Mass

Answer 8

-The mass of an object tells us the amount of matter in the object. The mass does not depend on where the object is. Mass is measured in Kg with a mass balance.

-Weight is the force acting on an object due to gravity. Because weight is a force, the unit of weight is the newton. It can be measured using a newtonmeter.

-The weight of an object depends on the strength of the gravitational field at the location of the object. The single point in an object where the weight is considered to act is called the centre of mass.

Question 9

Give the Calculation for Weight

Answer 9

Weight (N) = Mass (kg) x Gravitational Field Strength (N/Kg)

W = mg

-Weight and mass are directly proportional.

-The gravitational field strength on Earth is around 9.8 N/Kg
and on the moon is around 1.6 N/Kg.

Question 10

Describe what is Meant by the Resultant Force

Answer 10

-When several forces are acting on an object, we could replace all of the forces with a single force which has the same effect.

-Scientists call this single force the resultant force.

-If the forces are acting in parallel to each other then we simply subtract the smaller force from the larger force.

-If all the forces acting on an object give a resultant force of zero, the object is in equilibrium.

-When the forces are acting on an angle, we draw a vector diagram.

Question 11

Describe how to Draw a Vector Diagram

Answer 11

-Draw one arrow horizontally with a ruler to scale.

-Use a protractor to draw the other arrow at the given angle.

-Label the arrows with the given quantities.

-Complete the parallelogram with dotted lines.

-Measure the distance between the top right and bottom left angles. This distance is the resultant force.

Question 12

Describe what Happens when a Resultant Force Moves

Answer 12

-When a force moves an object through a distance, energy is transferred and work is done on the object.

-To make something move, (or keep it moving), a force must be applied. The thing applying the force needs a source of energy.

-The force does ‘work’ to move the object and energy is transferred from one store to another.

Question 13

Describe the Energy Transfers Taking Place When a Boy Pulls a Sledge

Answer 13

-Tension in the rope transfers energy from the boy’s chemical energy store to the kinetic energy store of the sledge.

-The force of friction is acting between the ground and the boy pulling the sledge.

-Friction transfers energy from the kinetic energy store of the sledge to the thermal energy stores of the sledge
runners and the ground.

Question 14

Explain why the Temperature of the Brakes in a Car Increases when the Car Brakes

Answer 14

-The force of friction acts between the brakes and the wheels.

-Because of this, the kinetic energy store of the car has been transferred to the thermal energy store of the brakes.

-This causes the temperature of the brakes to increase.

Question 15

Give the calculation for Work Done

Answer 15

Work Done (J) = Force (N) x Distance (m)

W = fs

-Work done can be calculated in Joules or Newton-metres

Question 16

Describe how Objects Change Shape when a Force Acts Upon It

Answer 16

-When a force acts on an object, the object may change shape by bending, stretching or compressing.

-However, there must be more than one force acting to change the shape of a stationary object.

-If one force is applied to a stationary object, then the forces would be unbalanced and we would have a resultant force. This would cause the stationary object to move.

Question 17

What is an Elastic and an Inelastic Material

Answer 17

-An object has been elastically deformed if it can go back to its original shape and length after the force has been removed. Objects that can be elastically deformed are called elastic objects.

-An objects has been inelastically deformation if does not fully reverse when the force is removed - there is a permanent change in shape. Objects that behave like this are called inelastic objects.

Question 18

Describe the Energy Transfers when Someone Stretches or Compresses an Elastic Object

Answer 18

-When a person stretches or compresses an elastic object, chemical energy stores in the person’s muscles transfer to the elastic potential energy store in the elastic object.

-This is an example of work done. The total work done is equal to the energy transferred as long as the object is not inelastically deformed.

Question 19

State Hooke’s Law

Answer 19

The extension of a spring (or any elastic material) is directly proportional to the force applied.

Question 20

Give the Calculation for the Force Needed to Compress or Stretch an Object

Answer 20

Force (N) =Spring Constant (N/m) x Extension (m)

F = ke

Question 21

What is Meant by the Spring Constant

Answer 21

-Spring constant is a measure of the stiffness of a spring up to its limit of proportionality.

-The limit of proportionality refers to the point beyond which Hooke’s law is no longer true when stretching a material

-The higher the spring constant, the stiffer the spring. The spring constant is different for different elastic objects.

-For a given spring and other elastic objects, the extension is directly proportional to the force applied.

Question 22

What is Meant by the Elastic Limit of an Object

Answer 22

-The elastic limit of a material is the furthest point it can be stretched or deformed while being able to return to its previous shape. It is also called the limit of proportionality.

-When an elastic object is stretched beyond its elastic limit, the object does not return to its original length or shape when the force is removed.

-Once a material has gone past its elastic limit, its deformation is said to be inelastic.

Question 23

Describe a Method for the Investigating Springs Required Practical

Answer 23

-Secure a clamp stand to the bench using a large mass on the base. Use bosses to attach two clamps to the clamp stand. Attach the spring to the top clamp, and a ruler to the bottom clamp.

-Adjust the ruler so that it is vertical, and with its zero level with the top of the spring. Measure and record the unloaded length of the spring.

-Hang a 100 g slotted mass carrier from the spring. Measure and record the new length of the spring.

-Add a 100 g slotted mass to the carrier. Measure and record the new length of the spring. Repeat the method until you have added a total of 1,000 g.

-Record the results in a table and use them to plot a force-extension graph.

Question 24

How does the Large Mass on the Base of the Clamp Stand Make the Investigating Springs Required Practical Safer

Answer 24

-In this practical, we are hanging weights from the spring.

-At some point, the weight that we add could be enough to make the apparatus topple.

-If this happens then the weight could land on our feet.

-To stop this, we place a heavy weight on the clamp stand.

Question 25

Why is it Important to Keep the Ruler Straight in the Investigating Springs Required Practical

Answer 25

-In this experiment, the metre rule must be kept vertical and the pointer must be kept horizontal. -This helps to make the results accurate. Accurate results are close to the true value.

Question 26

Describe how to Work Out the Extension of the Spring in the Investigating Springs Required Practical

Answer 26

To work out the extension of the spring, we take the value with the weight added and subtract the value when no weight is added.

Question 27

Describe how to More Certainly Find the Limit of Proportionality in the Investigating Springs Required Practical

Answer 27

-Because we are adding 1 N weights to the spring, we cannot be certain of the exact point where we exceed the limit of proportionality. -The way to address this is to add 0.1 N weights. This will allow us to more accurately pinpoint the weight where we exceed the limit of proportionality.

Question 28

Describe what is Meant by a Moment

Answer 28

A moment is the turning effect of a force.

Question 29

Give the Calculation for Moments

Answer 29

Moment (Nm) = Force (N) x Distance from Pivot to Line of Action of Force (m) M = Fd -The distance from the pivot to the line of action of the force may also be called the perpendicular distance. -This is when the distance from the pivot is at right angles to the line of action of the force.

Question 30

Explain why Turning a Nut is Easier with a Longer Handled Spanner

Answer 30

-If we increase the length of the spanner handle, we increase the distance between the pivot and the line of action of the force. -This increases the moment, making it easier to turn the nut.

Question 31

Describe how a Wheelbarrow Could be Designed to make Lifting the Load Easier

Answer 31

-The wheelbarrow could be redesigned with a longer handle. This would increase the distance from the pivot to the line of action of force. -The moment equals the force multiplied by the distance from the pivot to the line of action of the force. -With a longer handle, we could achieve the same moment by applying a smaller force.

Question 32

Explain why a Screwdriver with a Thicker handle will be Easier to Use

Answer 32

-A screwdriver with a thick handle will require less force to turn the screw than a screwdriver with a thin handle. -This means that the distance from the pivot to the line of action of the force is greater with a thicker handle than a thinner one. -Because of this, we will need to apply a smaller force to the screwdriver with a thicker handle than to the screwdriver with a thinner handle in order to achieve the same moment.

Question 33

Describe the Moments in a balanced Object

Answer 33

If an object is balanced, the total clockwise moment about a pivot is equal to the total anticlockwise moment about that pivot.

Question 34

Explain what Must happen for a Crane to Carry a Mass Greater than its Own

Answer 34

-If the crane is lifting a greater mass then the anticlockwise moment due to weight will increase. -To balance the crane, we will need to increase the clockwise moment due to the counterweight. -We cannot increase the mass of the counterweight so to increase the clockwise moment, we need to increase the distance between the counterweight and the pivot.

Question 35

Describe the Purpose of Gears

Answer 35

-Gears have teeth which interlock so that turning one causes another to turn, in the opposite direction. -They are used to transmit the rotational effect of a force from one place to another. -Different sized gears can be used to change the moment of the force. A force transmitted to a larger gear will cause a bigger moment, as the distance from the pivot is greater. -The larger gear will turn slower than the smaller gear.

Question 36

Describe what is Meant by Pressure

Answer 36

Pressure is the force per unit area

Question 37

Give the Calculation for Pressure

Answer 37

Pressure (Pa) = Force (N) / Area (m^2) P = F/A

Question 38

Explain why When Doing a Handstand, the Pressure is Greater than When Standing Upright

Answer 38

-The weight is unchanged. -The area of the hands is less than the area of the feet so the pressure on the hands during the handstand is greater than the pressure on the feet when upright.

Question 39

Explain why Snow Shoes are Useful for Walking Across Snow

Answer 39

-The contact area of snow shoes is greater than the contact area of soles of feet. -Pressure equals weight divided by area so wearing snow shows means there is less pressure on the snow making them easier to walk in.

Question 40

Explain how Particles in Fluids Produce a Pressure on the Walls of the Container

Answer 40

-When particles in a fluid collide with the walls of the container, they exert a force. -This force acts at right angles to the surface of the wall.

Question 41

Explain why the Pressure of the Atmosphere is Less at Higher Altitudes than the Earth's Surface

Answer 41

-At higher altitudes the air is less dense than at sea level. This means that there are fewer particles per cubic metre of air. -Because of this, the force exerted on a surface by the gas particles will be lower at higher altitude than at sea level. -The pressure of a gas is due to the force exerted by the gas particles on the walls of the container. This means that gas pressure is lower at higher altitudes than at sea level.

Question 42

Explain why Mountaineers Take a Supply of Oxygen When they Climb Very Tall Mountains

Answer 42

-The atmospheric pressure is low on tall mountains (ie at high altitude). This means that the number of gas particles per cubic metre is lower than it would be at sea level. -Because of this, climbers may not be able to take in enough oxygen from the atmosphere for their body's needs. To help with this, climbers often take a supply of oxygen.

Question 43

Explain why Crisp packets Expand in Aeroplanes

Answer 43

-Crisp packets are full of gas. These gas particles collide with the walls of the crisp packet, applying a force. -When the airplane is on the ground, the air pressure outside the crisp packet is the same as the gas pressure inside the crisp packet so the forces balance. -However, when an airplane is flying, the air pressure in the cabin is lower than on the ground. -This means that the pressure due to gas inside the crisp packet is greater than the pressure of the air in the cabin. Now the forces are unbalanced and the crisp packet expands.

Question 44

Give the Calculation for Pressure in Liquids

Answer 44

Pressure (Pa) = Height of Column (m) x Density of the Liquid (Kg/m^3) x Gravitational Field Strength (N/Kg) p = hρg

Question 45

Explain why the Walls of a Dam Needs to be Stronger at the Base

Answer 45

-The pressure at the base will be greater than the pressure near the top because the base has a greater force of weight acting upon it so the bottom of the wall needs to be thicker to hold the pressure.

Question 46

Describe how Pressure in a Liquid Changes with Depth

Answer 46

-The pressure of a liquid depends on the depth. A greater depth has a greater pressure. Because the bottom of an object is at a greater depth than the top, it experiences a greater pressure. -This means that the bottom of an object experiences a greater force than the top. Because of this, we have a resultant force acting upwards. Scientists call this upward force upthrust. -The upthrust is equal to the weight of fluid that has been displaced by the object.

Question 47

Describe how Upthrust Causes an Object to Float or Sink

Answer 47

-An object will float if the upthrust is equal to the weight of the object. This will happen if the object can displace its own weight of liquid. -An object that is denser than the fluid it is placed in is unable to displace enough fluid to equal the weight. This means that its weight is always larger than the upthrust so it sinks.

Question 48

Describe the Difference Between Distance and Displacement

Answer 48

-Distance is just how far an object has moved. It has magnitude (size) but no direction and is therefore a scalar quantity. -Displacement measure the distance and direction in a straight line from an object's starting point to its finishing point. It has both magnitude and direction which means that displacement is a vector quantity.

Question 49

Describe the Difference Between Speed and Velocity

Answer 49

-Speed is how fast an object is travelling with o regard to the direction. It has magnitude (size) but no direction and is therefore a scalar quantity. -Velocity is speed in a given direction. It has both magnitude and direction which means that velocity is a vector quantity.

Question 50

Give the Calculation for Speed

Answer 50

Distance (m) = Speed (m/s) x Time (s) s = vt

Question 51

Give the Typical Speeds of Different Everyday Objects

Answer 51

A person walking- 1.5 m/s A person running- 3 m/s A person cycling- 6 m/s A car- 13 m/s A train- 50 m/s A plane- 250 m/s Sound- 330m/s

Question 52

Describe what can Affect the Speed at Which a Person can Run

Answer 52

-A younger person will generally be able to achieve a faster speed than an older person. -A fitter person will be able to run faster than an unfit person. -A person running on flat ground will usually be able to run faster than a person running uphill. -A person who has only run a short distance should be able to run faster than a person who has already run a great distance.

Question 53

State what Happens to the Speed of Sound When the Air is Warmer

Answer 53

The speed of sound increases when the air is warmer.

Question 54

Explain why the Velocity of a Car Changes but the Speed remains Constant When Travelling Around a Roundabout

Answer 54

-When objects move in a circle, the object's velocity is constantly changing even though its speed is constant. -That is because velocity is a vector quantity so it has both magnitude (size) and direction. -For objects moving in a circle, their direction is constantly changing. -This means that their velocity is also constantly changing, even when their speed is constant.

Question 55

State what the Lines on a Distance - Time Graph Shows

Answer 55

-The line on a distance time graph shows the movement of the object. The steeper the graph, the faster the object is travelling at. -A straight line across shows that the object is stationary. -A straight uphill or downhill line shows the object is travelling at steady speed. -A line uphill is moving away from the starting point and a line downhill is moving towards the starting point. -A steepening curve means the object is speeding up and a levelling off curve means its slowing down. -If the object is accelerating, its speed at a certain point can be found by finding the gradient of the tangent to the curve.

Question 56

Describe what is Meant by Acceleration

Answer 56

Acceleration is the change in velocity in a certain amount of time.

Question 57

Give the Calculations for Acceleration

Answer 57

Acceleration (m/s^2) = Change in Velocity (m/s) / Time Taken (s) a = Δv / t Final Velocity (m/s) - Initial Velocity (m/s) = 2 x Acceleration (m/s^2) x Distance (m) v2 - u2 = 2as

Question 58

State what the Lines on a Velocity - Time Graph Shows

Answer 58

-The gradient on a velocity time graph shows the acceleration of the object. The steeper the line, the greater the acceleration or deceleration. -A straight line facing upwards shows a constant acceleration. A straight line facing downwards shows a constant deceleration. -A straight line across shows a steady speed. -A curved line shows a changing acceleration. -The area under the graph shows the distance travelled.

Question 59

Describe how Friction Causes Objects to Slow Down

Answer 59

-If an object has no force propelling it along, it will always slow down and stop because of friction. -Friction always acts in the opposite direction to movement. -To travel at a steady speed, the driving force needs to balance the frictional forces. -Friction happens between two surfaces in contact or when an object passes through a fluid.

Question 60

Describe how Drag is Different to Friction

Answer 60

-Drag is the resistance you get in a fluid (air resistance is a type of drag). -To reduce the effects of drag, the object's shape should be kept streamlined. This is when the object is designed to allow fluid to flow easily across it, reducing drag. -Frictional forces from fluids always increase with speed.

Question 61

Describe how a Skydiver Experiences Air Resistance

Answer 61

-A skydiver is an example of an object falling through a fluid. Initially, only the force of gravity is acting. -This causes the skydiver to accelerate towards the ground at 9.8m/s^2. However, as they fall, the skydiver experiences an upward force due to friction with air particles. This is called air resistance. -When air resistance balances gravity, the skydiver stops accelerating and moves at a constant velocity. This is called the terminal velocity.

Question 62

Explain why a Skydiver Reaches Terminal Velocity When Their Parachute is Closed

Answer 62

-When the skydiver leaves the airplane, only the force of weight is acting. The size of this force will not change. Because there is a resultant force, the velocity of the skydiver increases as they accelerate towards the ground. -As the skydiver falls, they collide with air particles. This causes the force of friction acting upwards. Because the air resistance is much smaller than weight, the skydiver continues to accelerate towards the ground. -As the skydiver's velocity increases, the air resistance increases. When air resistance balances the force of weight there is no resultant force. Now the skydiver moves down at a constant velocity.

Question 63

Explain why a Skydiver Reaches Terminal Velocity When They Open Their Parachute

Answer 63

-The skydiver now opens their parachute. Air resistance now massively increases. Air resistance is now much greater than weight so there is a resultant force acting upwards. This causes the skydiver to decelerate (their velocity decreases). -As the velocity decreases, the air resistance decreases. At some point, air resistance and weight are balanced. Now the skydiver moves downwards at a constant velocity. This is the new (lower) terminal velocity.

Question 64

Describe Newton's First Law of Motion

Answer 64

-If a resultant force of zero acts on a stationary object then the object will remain stationary. -If a resultant force of zero acts on a moving object then the object will continue moving in the same direction with the same speed.

Question 65

Explain why a Car Moving in a Straight Line at a Constant Speed will have a Resultant Force of Zero

Answer 65

-The car is moving in a straight line at a constant speed. -Because it is not changing in direction and is not changing in speed, the forces acting on the car must be balanced. -In other words the resultant force must be zero. -The resistive forces acting on the car are friction with the road and friction with air particles.

Question 66

Describe Newton's Second Law of Motion

Answer 66

The acceleration of an object is proportional to the resultant force and inversely proportional to the mass of the object.

Question 67

Give the Calculation for the Acceleration of an Object Due to a Resultant Force

Answer 67

Force (N) = Mass (Kg) x Acceleration (m/s^2) F = ma

Question 68

Describe what is Meant by Inertia

Answer 68

Inertia is the tendency of objects to either remain still or continue moving in the same speed and direction unless a resultant force is applied.

Question 69

Describe what is Meant by the Inertial Mass

Answer 69

-If we know the force needed to accelerate the object, we can use this to calculate the object's mass (using the equation Force = Mass x Acceleration). -Scientists call this mass the inertial mass because it was calculated from force and acceleration rather than from density.

Question 70

Describe how the Inertial Mass Affects the Force Needed to Produce a Given Acceleration

Answer 70

If an object has a larger inertial mass, it will require a greater force to produce a given acceleration compared to an object with a smaller inertial mass.

Question 71

Describe Newton's Third Law of Motion

Answer 71

Whenever two objects interact, the forces they exert on each other are equal in magnitude but opposite in direction.

Question 72

Give Examples of Newton's Third Law of Motion

Answer 72

-The wheels of a car exert a backwards force on the road. The road exerts a forward force on the wheels. -The Earth exerts a downwards force of attraction due to gravity on a skydiver. The skydiver exerts an upwards force of attraction due to gravity on the Earth. -A person uses a paddle to exert a backwards force into water. The water exerts a forwards push force onto the paddle.

Question 73

Describe a Method for the Acceleration Required Practical

Answer 73

-Set up a light gate on a table and connect it to a data logger. Set up a trolley so it holds a piece of card with a gap in the middle that will interrupt the signal on the light gate twice. -Connect the trolley to a string that goes over a pulley and is connected on the other side to a 100 g slotted mass carrier. Add ten 100g masses to the carrier. -Mark a starting line on the table so the trolley always travels the same distance to the light gate. Place the trolley on the starting line, holding it so the string is taut. Then, release it. -Record the acceleration measured by the light gate as the trolley passes through it. Repeat this twice more to get an average acceleration. -Now, place the trolley back on the starting line and transfer a 100g slotted mass from the carrier to the trolley. Release the trolley again and repeat twice more for an average. -Continue doing this up to 1000g and record the average acceleration for each force.

Question 74

Describe how to Investigate the Effect of Mass in the Acceleration Required Practical Rather than the Effect of Force

Answer 74

-In the second part of the experiment we change the mass of the toy car but we keep the force constant. -To do this we keep the weight on the end of the string constant but we add progressively greater masses onto the trolley.

Question 75

Explain why the Mass is Transferred from the Hook to the Trolley in the Acceleration Required Practical

Answer 75

-During the first part of this experiment, we are investigating the effect of changing the size of a force on the acceleration of an object of constant mass. -We change the force by removing masses from the end of the string. However, if we simply removed mass then we would be reducing the mass of the object. -So to prevent this, we have to take the mass that we remove from the string and place it on the toy car. -This way we have reduced the force but we have not changed the total mass.

Question 76

Describe the Effect of Decreasing the Force Applied While Keeping the Total Mass the Same on the Acceleration Required Practical

Answer 76

-Newton's Second Law of Motion states that the acceleration of an object is proportional to the force applied but inversely proportional to the mass of the object. -If we decrease the force applied (while keeping the total mass the same) then we will find that a smaller force will produce a smaller acceleration.

Question 77

Describe the Effect of Increasing the Mass While Keeping the Force Applied the Same on the Acceleration Required Practical

Answer 77

-Newton's Second Law of Motion states that the acceleration of an object is proportional to the force applied but inversely proportional to the mass of the object. -If we increase the mass (while keeping the force applied the same) then we will find that a greater mass leads to a smaller acceleration.

Question 78

Describe what is Meant by Thinking, Braking and Stopping Distance

Answer 78

-The thinking distance is the distance travelled by the vehicle during the driver's reaction time (ie the time taken for the driver to spot an obstruction, make a decision and move their foot to the brake). -The braking distance is the distance travelled by the vehicle from when the driver first applies the brakes to when the vehicle stops. -The stopping distance is the sum of the thinking distance and the braking distance. In other words, the distance a vehicle moves from when the driver first spots an obstruction to when the vehicle comes to a complete stop.

Question 79

Describe what is Meant by Ideal Conditions

Answer 79

-Ideal conditions mean that the driver is well rested, not distracted and not under the influence of any drugs such as alcohol. -The weather should also be dry with good visibility (for example no mist or fog). The car's brakes and tyres should also be in good condition (ie not worn).

Question 80

Describe the factors Affecting Thinking Distance

Answer 80

Speed- the faster the car is travelling, the further the car will travel during the time taken to react. Reaction Time- the longer the reaction time, the longer the thinking distance Other factors include: -consuming drugs or alcohol, using a mobile phone, how tired the driver is

Question 81

Describe the factors Affecting Braking Distance

Answer 81

Speed- for a given braking force, the faster the vehicle travels, the longer it takes to stop. The Weather or Road Surface- if it is wet or icy, there is less grip (so less friction) between a vehicle's tyres and the road, which can cause tyres to skid. Tyre Conditions- if the tyres of a vehicle are bald then they cannot get rid of water in wet conditions. This leads to them skidding on top of the water. Brake Conditions- if the brakes are worn or faulty, they won't be able to apply as much force as well maintained brakes, which could be dangerous when you need to break hard.

Question 82

Suggest why the Speed Limit is Often Reduced in Residential Areas

Answer 82

-Residential streets are more likely to present a driving hazard compared to a main road. -The stopping distance of a car increases at higher speeds. At 20 miles per hour, a driver will stop in a shorter distance than at 30 miles per hour. -Therefore it is safer to driver at 20 miles per hour (rather than 30 miles per hour) on a residential street.

Question 83

Explain why it is Dangerous to Drive too Closely to the car Infront

Answer 83

-The speed limit on many roads in the UK is 30 miles per hour. At this speed, if a driver braked fully, it would take six car lengths to stop. -Driving too closely to the car in front is dangerous because if they brake hard, it might not be possible for the driver behind to stop in time. This would cause a collision.

Question 84

Describe how a Car Brakes

Answer 84

-When a car brakes, the brake presses against the wheel. This causes the force of friction to act. -The kinetic energy store is transferred to the thermal energy store and the temperature of brakes increases as the car slows. -If we increase the speed of the car then a greater braking force is needed to stop the car in a given distance. -Braking while at high speed can cause the brakes to overheat or the driver to lose control of the vehicle.

Question 85

Describe what is Meant by Momentum

Answer 85

Momentum is a measure of how difficult it is for something to stop.

Question 86

Give the Calculation for Momentum

Answer 86

Momentum (Kg m/s) = Mass (Kg) x Velocity (m/s) p = mv

Question 87

Describe how Momentum Works in a Closed System

Answer 87

In a closed system, the total momentum before an event is equal to the total momentum after the event.

Question 88

Describe how Conservation of Momentum Affects Objects in a Crash

Answer 88

-When two objects crash, the object hit will move faster as it gains momentum from the crash. -The other object loses an equal amount of momentum because it is preserved. -Both objects exert equal and opposite forces on each other but there are no forces acting on them. Conservation of momentum applies when there are no external forces acting.

Question 89

Explain why a Cannon Recoils

Answer 89

-The total momentum of the cannon and cannonball before firing is 0 kg m/s. Momentum is always conserved so the total momentum of the cannon and cannonball must be 0 kg m/s after firing. -The cannonball has momentum in the forward direction. This means that the cannon must have momentum in the backward direction. -The forward momentum of the cannonball is cancelled by the backward momentum of the cannon. So the total momentum after firing is 0 kg m/s. -If the cannonball moves forwards then the cannon must move backwards in order for momentum to be conserved.

Question 90

Give the Calculation for Force when Momentum Changes

Answer 90

Force (N) = ( Mass (Kg) x Change in Velocity (m/s) ) / Time (s) F = (mΔv) / t

Question 91

Explain how Seatbelts Reduce the Risk of Serious Injury

Answer 91

-If the driver is wearing a seatbelt then the driver will come to a stop more gradually. Their momentum will fall to zero but over a much longer time. -This means that they will experience much lower forces than if they were not wearing their seatbelt. These forces could cause an injury but are less likely to prove fatal.

Question 92

Explain how Seatbelts Stretching Reduce the Force on Passengers

Answer 92

-Seatbelts are designed to stretch slightly when they are engaged. This stretching causes the driver to come to a stop more slowly than if the seatbelt was rigid. -Because of this, the driver's momentum will reduce more slowly, reducing the forces acting and reducing the risk of injury.

Question 93

Explain how Airbags reduce the Risk of Serious Injury

Answer 93

-Airbags deploy during a collision. These inflate so that as the driver moves forward, the driver's movement is cushioned by the airbag. This slows down the change in momentum and reduces the forces acting. -They are designed to inflate and then deflate. This means that when a driver collides with the airbag, the bag loses some of its gas, again slowing momentum change. -If the bag remained fully inflated, the driver would come to a stop more rapidly and experience greater forces.

Question 94

Explain the Benefit of using Polystyrene in Helmets Rather than Using a Rigid Helmet

Answer 94

-The purpose of a cycle helmet is to slow down the change in momentum of the cyclist's head during a collision (thereby reducing the forces acting). -Helmets contain expanded polystyrene. During a collision, the cyclist's head presses on the polystyrene. This crushes the polystyrene and slows down the rate of momentum change. -A rigid helmet would not slow down momentum change as effectively so the forces acting would be greater and would be more likely to cause injury.

Question 95

Explain why Crash Mats are used in Playgrounds

Answer 95

Crash mats increase the time taken for the impact which reduces the change in momentum thereby decreasing the force felt by the children.