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GCSE OCR Physics- Triple > Topic P2- Forces > Flashcards

Topic P2- Forces Flashcards

1
Q

What is the difference between distance and displacement?

A
  • they both measure how far something has travelled,

- but displacement also says which direction something has travelled in.

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2
Q

What are scalar quantities?

A

-Scalar quantities have a size or magnitude only and need no other information to specify them.

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3
Q

Give examples of some scalar quantities:

A
  • speed
  • distance
  • mass
  • time
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4
Q

What are vector quantities?

A

Vector quantities have both magnitude and an associated direction.

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5
Q

Give examples of some vector quantities:

A
  • velocity
  • displacement
  • force
  • acceleration
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6
Q

What is the equation for calculating displacement?

A

displacement (m) = velocity (m/s) x time (s)

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7
Q

What is the equation for calculating distance travelled?

A

distance travelled (m) = speed (m/s) x time (s)

d ---------- s   x   t
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8
Q

What is acceleration?

A
  • It is how quickly the velocity is changing.
  • The change in velocity can be a CHANGE IN SPEED
  • The change in velocity can be a CHANGE IN DIRECTION
  • or BOTH
  • Acceleration is like velocity; it is a vector and can have a positive or negative value.
  • If an object has negative acceleration, it is either slowing down (decelerating) or speeding up in the negative direction.
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9
Q

What is the equation for calculating acceleration?

A

acceleration (m/s^2) = change in velocity (m/s) ÷ time (s)

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10
Q

How can you calculate the change in velocity?

A

Always do final velocity - initial velocity

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11
Q

Describe the acceleration of an object travelling in a circle at a constant speed:

A

An object travelling in a circle at a constant speed has changing velocity (because it is always changing direction) so it is always accelerating.

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12
Q

How can you calculate the distance or velocity of an object that is travelling at uniform acceleration?

A

(final velocity)^2(m/s)^2. - (initial velocity)^2(m/s)^2. = 2 x acceleration(m/s)^2. x distance(m)

OR!!

v^2 - u^2 = 2 x a x d

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13
Q

Describe an experiment used to investigate the relation between distance, speed and acceleration:

A

1) Set up apparatus (pg23) mark line on the ramp before the first light gate (makes sure the trolley starts from the same point each time)
2) Measure the distances between light gates 1 and 2, and 2 and 3.
3) Hold the trolley still at the start line and let it go- it will roll down the slope.
4) As it rolls down, it will accelerate. When it reaches the runway, it will travel at a constant speed (ignore friction!)
5) Each light gate will record the time when the trolley passes through it
6) The time it takes to travel between 1 and 2 can be used to calculate the average speed on the ramp,
7) and between gates 2 and 3 gives the speed on the runway (speed= distance ÷ time)
8) The acceleration of the trolley on the ramp can be found using acceleration = change in speed ÷ time
9) The initial speed of the trolley (=0 m/s)
10) The final speed of the trolley (equals the speed of the trolley on the runway)
11) the time it takes the trolley to travel between light gates 1 and 2.

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14
Q

Using the experiment where a trolley is rolled down a ramp to investigate the relation between distance, speed and acceleration, what variables in the experiment could you change to increase the final speed of the trolley?

A
  • the trolley’s acceleration on the ramp and its final speed on the runway will increase when the angle of the ramp increases
  • or the amount of friction between the ramp and the trolley decreases.
  • Increasing the distance between the bottom of the ramp and where the trolley is released will also increase the final speed of the trolley.
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15
Q

What do distance-time (d-t) graphs tell you about how far something has travelled?

A
  • The gradient at any point gives the speed of the object
  • Flat sections are where it’s stopped
  • A steeper graph means it’s going faster
  • Curves represent acceleration
  • A steepening curve means it’s speeding up (increasing gradient)
  • A levelling off curve means it’s slowing down (decreasing gradient)
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16
Q

What do velocity-time (v-t) graphs tell you about acceleration?

A
  • Gradient = acceleration
  • Flat sections represent steady velocity
  • The steeper the graph, the greater the acceleration or deceleration
  • Uphill sections (/) are acceleration
  • Downhill section () are deceleration
  • A curve means changing acceleration
  • The area under any section of the graph is equal to the distance travelled in that time interval.
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17
Q

In a velocity-time graph, how can you find the distance-travelled?

A

-The distance travelled in any time interval is equal to the area under the graph.

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18
Q

What is a contact force?

Give an example of a contact force:

A
  • To exert a contact force, two objects must be touching, e.g. pushing or pulling an object.
  • Friction is a contact force- as an object is being pushed a long a surface, there will be friction acting on it in the opposite direction.
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19
Q

What is a non-contact force?

Give examples on non-contact forces:

A
  • Non-contact forces are forces between two objects that aren’t directly touching.
  • For example, electrostatic, magnetic and gravitational forces.
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20
Q

What is an interaction pair?

A

-An interaction pair is a pair of equal and opposite forces acting on two different objects. (Example of Newton’s Third Law)

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21
Q

What is a resultant force?

A

The overall force on a point or object

-it has the same effect on the motion as the original forces acting altogether.

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22
Q

What do free body diagrams show?

A

A free body diagram is a diagram of an object with arrows drawn to show the direction and size of the forces acting on the object.

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23
Q

What does a resultant force of zero mean?

A

-An object with a zero resultant force will either be stationary or moving at a steady speed.

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24
Q

What does a non-zero resultant force mean?

A
  • If there is a non-zero resultant force on an object, then it will either accelerate or decelerate.
  • This is because the forces are unbalanced
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25
Q

When is an object in equilibrium?

A

When all the forces on it are balanced.

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26
Q

What is Newton’s First Law?

A

An object will remain stationary or at a constant velocity unless acted upon by an external resultant force.

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27
Q

What is Newton’s Second Law?

A

If an object is acted on by an external resultant force, the object will accelerate in proportion with the size of the force and in the direction of the force.

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28
Q

What is Newton’s Third Law?

A

When two objects interact, the forces they exert on each other are equal and opposite.

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29
Q

What is the formula to calculate the resultant force?

A

Force (N) = mass (kg) x acceleration (m/s^2)

F= ma

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30
Q

Describe an experiment which can be used to investigate Newton’s Second Law:

A

1)The acceleration of a trolley on air track can be used to investigate Newton’s Second Law
2)The force acting on the trolley is equal to the weight
(W = M x g) of the hanging mass
3) The hanging mass is released pulling the trolley along the track
4)By measuring the time and speed at which the trolley passes the light gates, the acceleration can be calculated.
5) You can increase the force acting on the trollye by moving one of the masses from the trolley to the hanging mass, and repeating the experiment
6)If you plot your results on a graph of force against acceleration, you should get a straight line, proving that F = ma

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31
Q

What is friction?

A
  • When an object is moving, friction acts in the direction that opposes the movement
  • Friction makes objects decelerate and become stationary,
  • so you need a driving force to keep moving (thrust)
  • Friction occurs between two surfaces in contact (e.g. tyres and the road)
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32
Q

What is drag?

A

-drag occurs when an object passes through a fluid (e.g. boat through water). Air resistance is a type of drag.

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33
Q

What will happen to the velocity of an object if its driving force is..:

  • equal to friction force
  • greater than (>) friction force
  • less than (
A
  • Equal: the object will move at a steady speed
  • Greater than (>): the object will accelerate
  • Less than (
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34
Q

Explain how moving vehicles can reach terminal velocity:

A
  • When objects first set off they have more driving force than friction force (resistance),
  • so they accelerate.
  • But the resistance is directly proportional to the velocity of the object
  • resistance ∝velocity
  • So, as the velocity increases, the resistance increases as well
  • This gradually reduces the acceleration until the friction force is equal to the driving force
  • so it doesn’t accelerate any more.
  • The forces are balanced (no resultant force).
  • The object will have reached its maximum velocity
  • or terminal velocity.
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35
Q

During free fall, how does a skydiver reach terminal velocity?
What if the skydiver opens his parachute?

A

1) At the start of a skydive the air resistance is SMALL so he accelerates downwards.
2) As his speed increases the drag-force due to the air increases.
3) Eventually the air resistance is big enough to BALANCE the skydiver’s weight. At this point the forces are balanced so his speed becomes CONSTANT
4) This is called terminal velocity

5) When the skydiver opens his parachute the air resistance suddenly INCREASES, causing him to start slowing down.
6) Because he is slower, his air resistance DECREASES again until it balances his weight.
7) The skydiver has now reached a new, lower Terminal Velocity.

36
Q

Why does opening a parachute help to slow down a skydiver who is free-falling?

A

1) With the parachute open, there is more air resistance (at any given speed)
2) because the skydiver’s area is larger
3) but the driving force (his weight) is the same.
4) This means his terminal velocity is much smaller (~15mph)
5) which is a safe speed to hit the ground at.

37
Q

What is inertia?

A

The natural tendency for objects to resist changes in their velocity.

38
Q

What characteristics of an object affect the size of intertia?

A
  • Inertia is dependent on the mass of the object
  • The larger the mass, the larger the inertia
  • so the harder it is to change the velocity of the object.
  • By rearranging the equation for Newton’s Second Law you can show that mass is defined as the ratio of the force divided by acceleration.
  • So a larger mass requires a larger force to accelerate by a certain amount.
  • So it has a larger intertia.
39
Q

What is the equation to calculate inertial mass?

A

mass = force ÷ acceleration

40
Q

What is momentum?

A

Momentum:

  • is the product of mass.
  • and velocity.
  • Momentum is also a vector quantity
  • this means it has both a magnitude (size and direction)
41
Q

What is the formula to calculate momentum?

A

momentum (kg m/s) = mass (kg) x velocity (m/s)

42
Q

Using Newton’s 2nd Law, explain how force causes change in momentum:

A

-When a resultant force acts on an object for a certain amount of time
-it causes a change in momentum
-Newton’s 2nd Law can explain this:
-a resultant force on an object causes it to accelerate: force = mass x acceleration
-acceleration is just a change in velocity over time, so:
force = (mass x change in velocity) ÷ time
-this means a force applied to an object over any time interval will change the object’s velocity

43
Q

What is the equation for force and momentum?

A

force (N) = change in momentum (kg m/s) ÷ time (s)

or

F = P ÷ t

44
Q

If the change of momentum takes place over a small period of time, what happens to the size of the force?

A
  • The faster a given change in momentum happens,
  • the bigger the force causing the change must be
  • If ‘t’ in the equation is smaller,
  • then ‘F’ in the equation increases in size
  • in other words, ‘t’ is directly proportional to ‘F’
45
Q

What is the law of conservation of momentum?

A
  • In a collision when no other external forces act,
  • momentum is conserved
  • i.e. the total momentum after the collision
  • is the same as it was before it.
46
Q

Explain rocket propulsion in terms of conservation of momentum:

A

-When a rocket is stationary, it has zero velocity and so zero momentum
-If the rocket’s engines then fire
-it will produce a large amount of exhaust gases out backwards (negative momentum)
-since momentum is always conserved
-this means that the rocket has to move forwards
(positive momentum)
-in order to keep the combined momentum of the gases and the rocket at zero

47
Q

What is an elastic collision?

A
  • An elastic collision is where the total energy in the kinetic energy stores of the objects colliding
  • is the same before and after the collision
  • (the energy in the kinetic energy stores is conserved
48
Q

What is inelastic collision?

A
  • Inelastic collision is where some of the energy in the kinetic stores is transferred to the other stores.
  • For example, energy can be transferred away by heating or by sound.
49
Q

What is gravity?

A

Gravity is a force of attraction between all masses

50
Q

How does the size of an object affect the strength of the gravitational field?

A

-The larger the object is, the greater the strength of its gravitational field.

51
Q

What is the gravitational field strength on Earth?

A

10 N/kg.

52
Q

What is weight?

A
  • The force acting on an object when it’s in a -gravitational field.
  • It’s measured in Newtons (N)
53
Q

What is the equation for calculating the gravitational force?

A 
gravitational force (N) = mass (kg) x gravitational field 
                                                             strength, g (N/kg)

OR

W = m x g

54
Q

Is the weight of an object the same on different planets?

Is the mass the same on different planets?

A
  • Weight is different on different plants as every planet has a different gravitational strength
  • Weight is the force acting on an object when it is in a gravitational field,
  • so the force acting on the objects will be different on different planets as the gravitational strength varies.
  • Mass is the amount of matter or substance that makes up an object.
  • This doesn’t change in different planets, as gravitational field strength doesn’t affect the mass of an object.
55
Q

What is gravitational potential energy store?

A
  • Gravitational potential energy is the energy an object has by virtue of its position above the surface of the Earth.
  • When an object is lifted, work is done.
  • When work is done in raising the height of an object, energy is transformed as a gain in the gravitational potential energy of the object.
56
Q

What is the equation for calculating gravitational potential energy?

A

potential energy = mass x height x gravitational field
strength, g
(J) (kg) (m) (N/kg)

57
Q

What is kinetic energy store?

A

A Kinetic store - energy is stored in a moving object, for as long as the object moves.

It depends on both the object’s mass and velocity.

58
Q

What is the formula for calculating the kinetic energy store?

A

kinetic energy = 0.5 x mass x (velocity)^2

(J) (kg) (m/s)^2

59
Q

What happens to the kinetic energy store if the mass of an object is doubled?

A

-The energy in the kinetic energy store is doubled

60
Q

What happens to the kinetic energy store if the velocity is doubled?

A

-The energy in the kinetic energy store is quadrupled (increases by a factor of 4)

61
Q

When is “work done”?

A

When a force makes an object move, energy is transferred and work is done.

62
Q

Explain how “work is done”:

A

1) Whenever an object moves, something else is providing a form of ‘effort’ to move it
2) The ‘something else’ putting in the effort needs a supply of energy
3) This could be through fuel, food, electricity etc.
4) It then does work by moving the object, and transfers the energy it receives (from fuel e.g.) to other stores
5) This energy could be transferred usefully, or it can be wasted.

63
Q

What is the formula for calculating work done?

A

Work Done = force x distance
(J) (N) (m)

OR

W = Fd

64
Q

When something applies a force to move another object, allowing work to be done, what is the relationship between the work being done and the kinetic energy store of the object that is moved, presuming there is no friction?

A
  • If a force is applied to move an object,
  • the work done on the object will be equal to the energy transferred to the kinetic energy store of the object
  • assuming there is no friction
65
Q

What is power a measurement of?

A
  • Power is a measure of how quickly work is being done.

- Power is the rate at which energy is transferred

66
Q

What is the formula for calculating power?

A

Power (W) = work done (J) ÷ time (s)

OR

P = W ÷ t

67
Q

What is deformation?

A
  • A change in shape due to the application of a force is a deformation.
  • When you apply forces to an object it can be stretched, compressed or bent- this is deformation.
68
Q

How many forces are required to deform an object?

A

At least 2 forces.

69
Q

What is elastic deformation?

A

When an object returns to its original shape after the forces are removed.

70
Q

What is plastic deformation?

A

When the object doesn’t return to its original shape when you remove the forces.

71
Q

How do you know when a spring is in equilibrium?

A

The spring isn’t stretching any further.

72
Q

Describe the forces on a spring when it is in equilibrium?

A
  • The downwards force on the mass (weight)

- is equal to size in the upwards force that the spring exerts on the mass

73
Q

What is a spring?

A
  • A spring is an object that can be deformed by a force
  • and then return to its original shape
  • after the force is removed.
74
Q

What is Hooke’s Law?

A

Within certain limits, the force required to stretch an elastic object

  • such as a metal spring
  • is directly proportional to the extension of the spring.
75
Q

What is the equation to calculate the force exerted by an elastic object?

A

Force exerted by a spring= extension x spring constant

(N) (m) (N/m)

76
Q

Describe an experiment used to investigate the extension of a spring:

A

1) Hang your spring from a clamp stand, without the masses added, but with the hook the masses hang form)
- then measure the spring’s length with a ruler- this is the spring’s original length

2)Weigh the masses and add them one at a time to the hook hanging from the spring, so the force on the spring increases.

3) After each each mass is added, measure the new length of the spring, then calculate the extension:
- extension = new length - original length

4)Plot the graph of force (weight) against extension and draw a line of best fit

5) A straight line of best fit is where the spring obeys Hooke’s law and the gradient = spring constant
- If you’ve loaded the spring with enough masses, the graph will start to curve.

77
Q

What is the equation to calculate the energy store in an object’s elastic potential energy store?

A

energy transferred=0.5x spring constant x (extension)2
in stretching
(J) (N/m) (m)^2

78
Q

What is a moment?

A

The Moment of a force is a measure of its tendency to cause a body to rotate about a specific point or axis.

79
Q

What is the equation used for calculating this size of the moment of the force given?

A

moment of a force (Nm) = force (N) x distance (m)

80
Q

What is the principle of moments?

A

Total anticlockwise moments=total clockwise moments

If the anticlockwise moments are equal to the clockwise moments, an object won’t turn.

81
Q

What is the purpose of a lever?

A
  • Levers transfer the turning effect of a force
  • push one end of a lever down and the rotation around the pivot causes the other end to rise.
  • Levers increase the distance from the pivot that the force is applied, so less input force is needed to get the same moment.
  • This moment provides an output force to a load.
  • Levers are known as force multipliers, they reduce the force needed to get the same moment.
  • E.g. wheelbarrows, scissors etc.
82
Q

What will be the effect of using a longer lever to apply a force further from the pivot?

A
  • The longer the lever, and the further the effort acts from the pivot,
  • the greater the force on the load will be.
  • It is easier to use a longer spanner when trying to turn a nut,
  • and easiest to push furthest from the hinge when opening a door.
83
Q

What are gears and how do they work?

A

1) A gear is a rotating circular machine part having cut teeth
2) The teeth of different gears can interlock so that turning one gear causes another to turn as well.
3) A gear spinning clockwise will make the next gear spin anticlockwise.
4) This alternates as you go from to gear to gear
5) A force applied to a small gear creates a small moment.
6) The small gear applies this force to the gear adjacent to it
7) If the second gear is larger, the force is being applied further from the pivot (of the larger gear)
8) so the moment of the larger gear is larger.
9) A series of gears that get bigger from gear to gear will multiply the moment of the first, smallest gear
10) Interlocked gears will rotate at different speeds, depending on their size
11) The larger the gear is, the slower it spins
12) For every complete turn of a small gear, a larger gear has only turned a small amount.
13) A gear’s radius is equal to the distance of the applied force from the pivot.

84
Q

How is pressure transmitted through a fluid?

A
  • Pressure in a fluid is transmitted equally in all directions
  • and it causes a net force at right-angles to any surface.
85
Q

How can you calculate pressure?

A

pressure (Pa) = force normal to a surface (N)
——————————————
area of that surface (m^2)

86
Q

What is a hydraulic system?

A
  • In a hydraulic system, pressure, applied to a contained fluid at any point, is transmitted undiminished.
  • That pressurised fluid acts upon every part of the section of a containing vessel
  • and creates force or power.
  • Due to the use of this force, and depending on how it’s applied, operators can lift heavy loads,
  • and precise repetitive tasks can be easily done.
87
Q

Describe how a simple hydraulic system works:

with a hydraulic system containing two pistons

A

1) Hydraulic systems are used as force multipliers
2) Eg. a hydraulic system may have two pistons,
- one with a small cross-sectional area
- one with a larger cross-sectional area
3) Pressure is transmitted equally though a liquid
4) So pressure at both pistons is the same
5) P = F ÷ A, so at the smaller piston a pressure is exerted on the liquid using a small force over a small area
6) This pressure is transmitted to the 2nd, larger piston
7) The 2nd piston has a larger area, and so F = P ÷ A, there will be a larger force.

GCSE OCR Physics- Triple (10 decks)

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