Forces Flashcards
1
Q
What are vector quantities?
A
A vector quantity has a magnitude and direction.
2
Q
What are examples of vector quantities?
A
- Force,
- Velocity,
- Displacement,
- Acceleration,
- Momentum.
3
Q
What are scalar quantities?
A
A scalar quantity has a magnitude but no direction.
4
Q
What are examples of scalar quantities?
A
- Speed,
- Distance,
- Temperature,
- Time
5
Q
How can two objects have a different velocity but be travelling at the same speed?
A
- Since speed is a scalar quantity, they can both have the same speed (length of the arrows) but be travelling in a different direction (the direction of the arrow),
- Velocity is vector quantity, this means that two objects moving at the same speed could have different velocities because they are travelling in different directions.
- A negative velocity moving backwards and a positive velocity moving forwards.
6
Q
What are the two types of forces?
A
- Contact,
- Non-Contact.
7
Q
What is a contact force?
A
A force that acts when two objects touch.
8
Q
What is non-contact force?
A
When the objects do not need to be touching for a force to act.
9
Q
What are some examples of a contact forces?
A
- Friction,
- Air resistance,
- Tension
10
Q
What area some examples of non-contact forces?
A
- Magnetic forces,
- Gravitational force,
- Electrostatic forces.
11
Q
What is an interaction pair?
A
A pair of forces that act on two objects, these forces act with equal strength in opposite directions.
12
Q
What is gravity?
A
- A force that every mass has, it attracts other masses towards it.
- It is only really noticeable on very large masses such as planets.
13
Q
What are the effects of the Earth’s gravity?
A
- It makes all masses fall towards the ground,
- It gives everything a weight.
14
Q
What is the difference between mass and weight?
A
- Mass is the quantity of matter in a body, weight is the force applied on a mass because of gravity.
- The mass of an object is always the same, however, weight will change depending on the gravitation field strength.
- For example, of earth, the gravity is 9.8 kg/NM but on the moon it is much less so we have less weight on the moon than on Earth.
15
Q
What is the relationship between mass and weight?
A
They are directly proportional,
weight = mass x gravity x height
16
Q
What do arrows show in a free body diagram?
A
The strength and direction of a force.
17
Q
What is the resultant force?
A
- The overall force of an object*
- In any object, when there is a force acting, there will always be one one acting in the opposite direction as well,
- The resultant force, subtracts the smallest force from the largest and shows the force in the stronger direction with an arrow in a free body diagram.,or as a value in Newtons.
18
Q
What happens when force moves an object through a distance?
A
Energy is transferred and work is done on the object.
19
Q
What happens when you push an object over a carpet (in terms of forces applied and energy transfer)?
A
- You are applying force and working against the friction that the carpet is applying to the object.
- Energy is transferred to the objects kinetic energy store because it moves.
- Some energy is also transferred to the thermal store because of the friction, this causes the object to heat.
20
Q
What is the equation involving work done, distance and force?
A
W = Fs
Work done = force x distance
J = N x m
21
Q
How do you find the resultant force of an object that has a force acting horizontal and vertical?
A
- First draw the vertical force to scale (3N = 3cm),
- Then draw the horizontal force to scale at the end of the vertical force,
- Draw a hypotenuse and find the length, that is the force in newtons,
- Find the angle a well and write the answer as:
(Force) (Bearing)
22
Q
What does it mean if an object is at equilibrium?
A
- The forces on either side of the object are equal,
- The object is either stationary (if it wasn’t moving originally),
- Or the object is moving at a constant velocity (if it was moving originally).
23
Q
What is magnitude?
A
The size of a quantity is it’s magnitude
24
Q
What is displacement?
A
This is distance without change.
25
What is Newton’s third law?
A law that states when two objects interact with each other, they exert equal and opposite forces on each other.
26
What is the unit of force?
Newtons
27
What happens to the force when a car moves?
The force of friction of the road on the tyre is in the forward direction
The force of the friction of the tyre on the road is in the reverse direction these two forces are equal and opposite.
28
What is Newton’s first law of motion?
If the forces acting on an object are balanced the resultant force on the object is zero. And if:
The object is at rest, it stays stationary
The object is moving, it keeps moving with the same speed and in the same direction.
29
What is an unbalanced force?
This is where the resultant force on an object is not zero, the movement of the object will depend on the size direction and resultant force
30
How can the moment of the force be increased on a spanner?
Increase the size of the force
| Using a longer handle on the spanner
31
What is the load?
This is the weight of the object
32
What is the effort?
This is the force you apply
33
What is the pivot/fulcrum?
This is the point where something turns
34
What is a lever?
It is something that includes a pivot which reduces the amount of effort you have to achieve to lift or move the load
35
What is the equation for moment of force?
Moment=force*perpendicular distance from the line of action of the force to the pivot
36
Give examples of force multipliers
Gears
| Levers
37
Why do you use a lever?
It multiplies the force as you get further away from the pivot the more the force
Becomes
38
Give some examples of levers?
Bottle opener
| A pair of scissors
39
What is a gear?
Gears multiply the moment of a turning effect by using a smaller gear to turn a larger gear.
40
What happens when a large gear turns a small one and vise vera?
- When a large gear turns a small gear, the turning effect is reduced (force applied) but the speed of the little gear is increased, so both gears have equal moment.
- When a smaller gear turns a larger gear, the turning effect increases, but the speed reduces, so both gears have equal moment.
41
What is the centre of mass?
The centre of mass of an object is the point at which its mass can be thought of as being concentrated
42
What is suspended equilibrium?
When you suspend an object the centre of mass will always come to rest with its centre of mass directly below the point of suspension
43
How to you find the centre of mass on a 2D object?
You would draw all the lines of symmetry and find the point where they all cross that is the centre of mass.
44
How do you find the centre of mass of a irregular shape?
1. Put a hole in one corner of the card and suspend the card from a rod
2. Use a plumbline to draw a vertical line on the card from the rod
3. Repeat the procedure, hanging the card from a different corner
The point where the two lines meet is the cards centre of mass.
45
What determines the moment on a see saw?
The weight of the person and the distance from the pivot.
| W1D1=W2D2
46
Why does an object stretch, bend or compress?
Because more than one force is acting on the object in different directions,
- For example, a spring would bend if there are forces pushing from one side at the top and another force pushing from the opposite side at the bottom.
47
Why does an object not stretch, bend or compress when force is only applied from one direction?
Because the object would simply be moved instead of bending/ stretching since the object does not have forces acting against each other.
48
What is an elastic object?
Any object that is elastically deformed.
49
What is elastic deformation?
When an object that is deformed returns to its original state after the force is taken away.
50
How can you test for the relationship between extension and force?
- Hang a spring,
- Measure the initial length of the spring
- Attach a weight onto the spring,
- Measure the new length of the spring,
- Plot weight (in Neutons) and difference in extension (m) and you will see that force is directly proportional to Extension.
51
What is the equation linking force, spring constant and extension?
```
F = ke
Force = Spring constant x Extension
(N) = (N/m) x (M)
```
52
What is the limit of proportionality?
- When two variables are no longer proportional,
- For example, extension and force have a limit of proportionality, when the spring stretches past this limit, it will not return back to its original state once the weight is removed.
53
How can you find the work done/ energy transferred if the spring does not pass its limit of proportionality?
E = 0.5 x k x e^2
elastic potential energy = spring constant x extension x 0.5
J = N/m x M x 0.5
54
What is a moment?
A force or forces that cause an object to rotate.
55
What is the equation for moment?
```
M = Fd
moment = force x distance
Nm = N x M
```
56
How do we maximise moment when rotating an object?
- Have a great distance between the pivot and force,
- apply the force at 90° in order to optimise the distance when you apply the force, as if the angle is less then the distance will decrease,
- Apply a large force.
57
When a weight is balancing on one side of the pivot, what must be true on the other side of the pivot?
It must have the same moment as the other side.
58
What is the advantage of using a lever instead just pushing an object?
Because their is a larger distance so the moment is greater than applying a force with a distance of 0, this is because M = Fm.
59
What are fluids?
Substances that can flow because their particles are able to move around.
60
What is pressure?
The force that has been applied over an area.
61
What happens when fluid particles collide in a container?
The particles apply a force that acts at a right angle to the walls.
62
Why does a crisp packet swell up on a plane?
- At ground level, the air pressure inside the bag is the same is outside the bag.
- However, in the cabin of an aeroplane, the air pressure is kept slightly lower than that at ground level,
- This means that the pressure inside the bag is greater than the pressure outside the bag so the bag inflates as mote force is pushing the bag outwards.
63
Where is the Earths atmosphere most dense?
At the surface, as you get further away from the surface, the atmosphere becomes less dense.
64
How does the atmosphere produce pressure?
Air molecules colliding with the surface,
| Force/ area.
65
Why does pressure decreases as the altitude raises?
There are less air molecules further up to collide so less pressure is made as less collisions can happen.
66
Why does a the water at the bottom of a container have more pressure than the top?
- There is more weight acting down on the bottom as there is more water above it,
- The top of the container has little weight acting down on it so its pressure is low.
67
What is the equation for pressure of a column of liquid?
```
Pressure = height x density x gravity
P = h x ρ x g
Pa = m x kg/m^3 x N/kg
```
68
What factors effect the pressure of a liquid?
- Depth,
- Density,
- Gravitational field strength.
69
What is upthrust?
A resultant force acting underneath an object in a liquid that pushes it upwards,.
70
Why do objects float?
- If the upthrust is equal to the objects weight, the object will float.
- If the object displaces the same amount of water as it weighs, then the upthrust is equal to its weight, as upthrust = weight of water displaced.
71
Why do objects sink?
If the upthrust is less than the weight of an object it sinks because the force acting up is too little to keep it on the surface.
72
What is the relationship between upthrust and displaced water?
The size of the upthrust force on an object is the same as the weight of the water displaced by the object.
73
Why does a more dense object sink in water?
- Density is mass/volume,
- A more dense object must have a greater mass/ volume than water,
- With more mass, this means the weight is higher over the same area,
- So the denser object cannot be forced upwards with upthrust because it cannot displace its own weight in water.
74
What is distance?
- It tells us the length of a route but with no direction,
| - It is a scalar quantity.
75
What is displacement?
- It tells us the distance that an object moves in a straight line,
- It has a magnitude and direction so is a vector quantity.
76
What is the equation for speed?
```
speed = distance/ time
v = s/t
m/s = m / s
```
77
What is the typical walking, running and cycling speeds?
- Normal walking speed = 1.5m/s
- Running speed = 3m/s
- Cycling speed = 6m/s
78
What are the typical speeds for a car (main road), train and cruising aeroplane?
- Car on main road = 13m/s
- Fast train = 50m/s
- Cruising plane = 250m/s
79
What is the speed of sound in air (typically)?
330m/s
80
What is velocity?
The speed of an object in a given direction.
| A vector quantity
81
What happens to the velocity of an object when moving round in a circle at a constant speed?
- Its velocity is always changing because its direction is changing even if the speed is constant.
82
What does the gradient of a distance-time graph show?
Velocity.
83
What does an upwards curve mean in a distance-time graph?
The speed is constantly increasing (acceleration)
84
How do you determine the speed of an accelerating object on a distance time graph?
Draw a tangent and work out the gradient of that.
85
What is acceleration?
The change in speed over a time period, m/s^2
86
What is negative acceleration also known as?
Deceleration.
87
What does the gradient of a velocity-time show?
The acceleration of the object.
88
How do you work out the distance using a velocity time graph?
Work out the area under the graph.
89
What is the equation for a acceleration if an object is accelerating at a constant rate?
v^2 - u ^2 = 2as
| final velocity - initial velocity = 2 x acceleration x distance
90
What is the initial acceleration of gravity?
9.8 m/s^2.
91
What is terminal velocity?
When an object falls from a height, it accelerates at 9.8 m/s^2,
- Then, the force of air resistance balances out the force of gravity and makes the object slow down its acceleration,
- Eventually, the object falls at a constant velocity and does not accelerate,
- This is terminal velocity.
92
Can terminal velocity be met in a liquid?
Yes, instead of air resistance, the force is upthrust.
93
What happens if the friction on a falling object is large?
The terminal velocity will be low because more force is slowing the falling.
94
What is Newton's first law?
If the resultant force is 0, then the object will either keep moving at a steady velocity, or stay stationary.
95
What is Newtons second law?
The acceleration of an object is directly proportional to the resultant force acting on an object and inversely proportional to the mass of the object.
F = am
a = f/m
96
What is the equation that links Force, acceleration and mass?
```
Force = acceleration x mass
F = am
N = m/s^2 x m
```
97
What is inertia?
Objects will stay still or keep the same motion unless a resultant force is applied to it.
98
What is the inertia mass?
A measurement of how difficult it is to change the velocity of an object.
An object with a large inertial mass will take more force to produce the same acceleration as an object with a lower inertial mass.
99
What is Newton's third law?
Whenever two objects interact, the forces they exert on each other are equal and opposite.
100
Give an example of Newton's third law?
When a rocket exhausts gases down, it applies a force,
| The ground forces back up equally, and pushes the rocket upwards.
101
What happens when a sky diver falls?
- As soon as he jumps from the plane the only force is gravity so he has a resultant force downwards and accelerates at 9.8 m/s^2,
- Then air resistance starts to act on him as he falls and slows down the acceleration, but the acceleration is still greater than the air resistance,
- As the skydiver accelerates the air resistance increases so balances out the force of the acceleration, until the air resistance = the weight,
- The skydiver will now fall at a constant velocity (terminal velocity),
- Then the sky diver will release their parachute and increase their surface area, this means that air resistance will increase a lot, and they will decelerate,
- Now the weight will balance out the air resistance, so the terminal velocity is lower and they fall to the ground safely..
102
How do you test for the effect of force on acceleration?
- First attach a rectangular cardboard cut out onto the top of a toy car with a known mass, the cardboard should have a gap in the middle of the rectangle so that it can break a light gates laser twice,
- Then place a light gate at a set distance away from a start line,
- attach the car to a pulley at the end of the table and have a hook with a weight on the other side of the string of the pulley,
- Then let go of the car from the starting line and see the acceleration using the software from the light gates,
- Repeat this 3 times, for each weight,
- Change the weight now: 1N, 2N, 3N, 4N and 5N.
- Using Newton's second law and using the equation v^2 - u^2 = 2as, you should find that force is proportional to the acceleration.
103
How do you find the effect of mass on acceleration?
- Set up the light gate acceleration practical,
- but this time, instead of changing the weight, add masses to the car: 100g, 200g, 300g, 400g and 500g.
- You should see that the acceleration is inversely proportional to the mass,
- The weight at the end of the pulley must be constant (1N for example).
104
What is stopping distance?
The distance it takes for a person to think and stop the vehicle after seeing a stimulus.
105
How does speed effect stopping distance?
The faster the speed the greater the stopping distance,
| speed is directly proportional to stopping distance.
106
What can increase reaction time?
- Alcohol and drugs
- Tiredness,
- Distractions
107
What is thinking distance?
The distance it takes for a driver to react to a stimulus on the road.
108
What is braking distance?
The distance it takes for someone to stop their vehicle.
109
What factors increase braking factors?
- Icy or wet conditions reduce friction so this increase braking distance,
- Braking distance will also increase with worn tires,
110
What happens when a car brakes in terms of energy transfer?
Kinetic energy is transferred to heat from the force of friction.
111
What happens to the kinetic energy of the car if the velocity is doubled?
Since E = 0.5 x m x V^2
| the velocity is squared so the energy is x4.
112
How do cars brake?
- There are brake pads press down on the wheel, they cause friction and slow down the wheels.
- The kinetic energy is now converted into thermal energy,
- The greater the speed the greater the force needed to stop the car.
113
What happens if the driver brakes to quickly?
- The brakes could overheat,
| - The driver could lose control of the car.
114
How can you estimate the force needed to brake a car?
Using the equation F = am
115
What is the equation linking mass, velocity and momentum?
Momentum = mass x velocity
P = m x v
kg m/s = kg x m/s
116
In a closed system, what is the difference in between momentum before and after an event.
There is no difference because no energy is lost or gained in a closed system.
117
What is the conservation of momentum?
The total momentum after an event is the same before the event.
118
When a cannon fires a ball, why is the total momentum zero?
- The ball is fired forwards and has momentum,
- The cannon is recoiled backwards and has equal momentum to the balls momentum,
- So the total momentum is zero, equal to the momentum before the ball was fired as there was no velocity before and anything x0 is 0.
119
How do you work out the velocity of two vehicles when they collide?
- Find the momentum of the vehicles,
- Add them together,
- Then add the masses of the vehicles together,
- Then divide the total momentum by the total mass and get a velocity.
120
How do you work out the force a vehicle after a crash (the momentum changes)?
```
F = ΔP / Δ time
P = m x Δv
```
121
How can we reduce the danger of force in a crash?
Increase the time that the force has to impact you (as the equation is divided by time).
122
How can we increase the time between the impact of crash?
- Airbags,
- Seat belts,
- Crash-mats
- Helmets,
- Cushioned surface.
