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Forces Flashcards

1
Q

What is a vector quantity? Name 3 examples

A

Quantities with magnitude and direction
Force, velocity, displacement

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2
Q

What is a scalar quantities? Name 3 examples

A

Quantities with only magnitude
Speed, distance, mass

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3
Q

What is a force?

A

A push or pull caused by an object interacting with something

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4
Q

What are contact forces? Name 3 examples

A

When two objects must be touching for a force to be exerted
Friction, air resistance, tension

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5
Q

What are non-contact forces? Name 3 examples?

A

When objects don’t need to be touching for a force to act
Magnetic force, gravitational force, electrostatic force

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6
Q

What is normal contact force?

A

Where a pair of forces are equal and opposite acting on two interacting objects

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7
Q

What is gravitational force?

A

The force of attraction between masses

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8
Q

What is weight? Close to earth, what is this caused by?

A

Weight is the force acting on an object due to gravity. Close to earth, this force is caused by the gravitational field around the earth

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9
Q

What is the centre of mass?

A

Where we think of a force as acting from a single point on the object, because we assume that that point is where its whole mass is concentrated

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10
Q

What is the relationship between mass and weight?

A

They are directly proportional

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11
Q

What is a free body diagram?

A

A diagram to show all the forces acting on an object, but none of the forces that object exerts on its surroundings

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12
Q

On a free body diagram, what do the arrows show?

A

The sizes of the arrows show the relative magnitudes of the forces
The direction o the arrows show the directions of the forces acting on the object

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13
Q

What is the resultant force?

A

The overall force on a point or object, or a single force with the same effect of all the original forces together

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14
Q

What happens when a force moves an object through a distance?

A

Energy is transferred and work is done on the object

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15
Q

What is equilibrium?

A

When all of the forces acting on an object combine to give a resultant force of zero

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16
Q

What three things can happen to an object when more than one force acts on an object?

A

You may cause it to stretch, compress or bend

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17
Q

Define elastic deformation?

A

An object has been elastically deformed if it can go back to its original shape and length after a force has been removed

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18
Q

Define inelastic deformation?

A

An object has been inelastically deformed if it doesn’t return to its original shape and length after the force has been removed.

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19
Q

What is the extension of a spring?

A

The difference between a springs length before and after a force is applied

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20
Q

What is the spring constant?

A

How many newtons it would take to extend an object by 1m

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21
Q

What does the spring constant depend on?

A

It depends on the material you stretch. The stiffer the material, the greater the spring constant

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22
Q

What is the limit of proportionality?

A

The maximum force that can be applied where force is proportional to extension

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23
Q

On a force-extension graph, what is the gradient?

A

The spring constant

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24
Q

On a force extension graph, what is the area under the graph until the limit of proportionality?

A

The energy stored in the elastic potential energy store.

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25
What is a moment?
The turning effect of a force
26
Describe how moments work with this diagram
The force on the spanner causes a turning effect, or moment, on the nut (the pivot). A larger force or a larger distance (longer spanner), would cause a larger moment For the maximum moment, you need to push at right angles to the spanner Pushing at any other angle results in a smaller distance and therefore a smaller moment.
27
How do levers work?
Levers increase the distance from the pivot at which the force is applied, meaning less force is needed for the same moment
28
How do gears work?
Gears are circular discs with teeth around their edges. The teeth interlock so that the turning one makes the other spin in the opposite direction, which transmits the rotational effect of a force from one place to another. Different sized gears change the size of the moment - e.g. a force transmitted to a larger gear causes a bigger moment, as the distance from the pivot is increased. The larger gear also turns slower than the smaller gear.
29
What is Hooke's Law? What is its equation?
The extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. The equation for Hooke's Law is: Force = spring constant x extension
30
What is pressure and what does this mean?
Force per unit area, meaning the particles exert a pressure
31
Explain how fluid exerts pressure?
A force is exerted normal (at right angles) to any surface is contact with the fluid
32
What does pressure in a liquid depend on?
Depth and density
33
What is true of liquids concerning density?
The density is the same everywhere and it doesn't vary with shape or size
34
What is density?
A measure of the compactness of a substance, or how close together the particles ina substance are
35
The denser a liquid, the _____ the pressure? Why?
The denser a given liquid, the more particles it has in a certain space. This mean there are more particles able to collide with each other and the surfaces, so pressure is higher
36
As the depth of a liquid increases, pressure ______? Why?
As depth increases, the number of particles above that point increases. The weight of the particles adds to the pressure at that point, so pressure increases with depth
37
How does upthrust work?
1. When an object is submerged in an fluid (completely or partially), the pressure of the fluid exerts a force on it in every direction. 2. Because pressure increases with depth, the force exerted on the bottom is greater than the force acting on the top of the object 3. This causes a resultant force upwards, known as upthrust.
38
What is upthrust equal to?
Upthrust is equal to the weight of the **fluid** that has been displaced by the object
39
When does an object float?
If the upthrust on an object is the the same as the weight of the **object**, the 2 forces balance and the object floats. The object is less dense than the fluid, so weighs less than the equivalent volume of fluid. Therefore, it displaces a volume of fluid equal to its own weight **before** It is completely submerged
40
When does an object sink?
When the object's weight is a larger force than the upthrust, it sinks. The object is more dense than the fluid, so weighs more that it's equivalent volume of fluid. Therefore, it displaces a volume of fluid that weighs less than its own weight, and can never displace a volume equal to it's own weight.
41
How is atmospheric pressure created on a surface
Air molecules colliding with the surface
42
As height increases, atmospheric pressure ______? Why?
As altitude increases, atmospheric pressure decreases This is because as height increases, the atmosphere gets less dense so there are fewer air molecules able to collide with the surface. There are also fewer air molecules above a surface as height increases, meaning the weight above the surface decreases, decreasing overall pressure.
43
What is distance?
Scalar quantity measuring how far an object has moved, regardless of a direction
44
What is displacement?
Vector quantity measure distance and direction in one straight line, relative to a starting/finishing point
45
If an object moves 5m north and 5m south, what is its distance travelled vs its displacement?
Distance is a total of 10m, but displacement is 0m (its gone forwards and backwards to the same point)
46
List typical everyday speeds that apparently you need to know What are the speeds of: person walking, running, cycling, a car, a plane, a train
Walking - 1.5m/s Running - 3m/s Cycling - 6m/s Car - 25m/s Plane - 250m/s Train - 55m/s
47
What are some factors affecting the speed of a human?
e.g. fitness level, age, distance travelled, terrain
48
What are the factors affecting speed of sound?
The materials the sound waves travel through
49
List factors affecting wind speed
Temperature, Atmospheric pressure, obstacles e.g large buildings, forestry
50
What is acceleration?
The change in velocity in a certain amount of time
51
What are the units for acceleration?
m/s^2
52
What is uniform acceleration the same as?
Constant acceleration
53
What is the gradient on a distance time graph?
On a distance time graph, gradient = speed
54
What are curves on a distance-time graph?
Acceleration or deccelaration
55
What are the gradients on an velocity time graph?
Acceleration
56
What are flat sections on a velocity time graph?
Constant speed
57
What are curves on a velocity time graph
Changing acceleration
58
What is the area under the graph equal to?
At any point, it is the distance travelled
59
Which direction does friction always act in?
Friction always acts in the opposite direction to movement
60
When do you get friction?
When two surfaces are in contact or when an object passes through a fluid
61
What is drag?
The resistance you get in a fluid (a gas or a liquid)
62
Name a type of drag?
Air resistance is a type of drag
63
What is air resistance?
The frictional force of air acting on a moving object
64
Explain how to reduce drag
The most important factor is streamlining. This where the object is designed to allow fluid to flow easily across it, which reduces drag.
65
What is a device that aims to increase drag?
Parachutes
66
As speed increases, drag _________?
As speed increases, frictional forces from fluid (drag) always increases
67
When objects fall through fluids, what do they eventually reach?
Terminal velocity
68
Explain how objects reach terminal velocity?
1. Falling objects initially experience a force of gravity much more than the frictional force slowing them down, so they accelerate. 2. As speed increases, friction increases 3. This reduces the acceleration until the frictional force is equal to the accelerating force, making the resultant force zero 4. This is when it reaches its terminal velocity, where with no changes, the object will fall at a steady speed.
69
How is terminal velocity decreased?
e.g. Parachutes 1. When a parachute is opened, air resistance increases greatly, but the force pulling the object down is still the same 2. This causes the object to decelerate until the forces become balanced again, but at a lower velocity.
70
What is Newton's first law?
If the resultant force on a stationary object is 0, it remains stationary. If resultant force on a moving object is zero, it remains travelling at a constant velocity
71
What does a non-zero resultant force always produce?
Acceleration or deceleration in the direction of the force
72
What are the 5 different forms that acceleration can take?
Stopping, starting, slowing down, speeding up and changing direction
73
Describe the relationship between acceleration and the resultant force
The larger the resultant force, the more an object accelerates The force and acceleration are directly proportional
74
Describe the relationship between acceleration and mass
(For a fixed resultant force) An object with a larger mass accelerates less than one with a smaller mass Acceleration is therefore inversely proportional to mass
75
What is inertia?
The tendency for motion to remain unchanged, or to continue in the same state of motion
76
What is inertial mass?
A measure of how difficult it is to change the velocity of an object
77
How is inertial mass calculated?
Using Newton's second law. It can be rearranged to give m = F / a So inertial mass is just the ratio of force over acceleration
78
What is Newton's third law?
When two objects interact, the forces they exert on each other are equal and opposite.
79
Explain Newton's third law using the image
- Skater A feels an equal and opposite force from skater B when they push against each other - Both skaters feel the same sized force in opposite directions, so accelerate away from each other - Skater A is accelerated more than B because she has a smaller mass - this is because a = F / m, so smaller mass means larger acceleration (inversely proportional)
80
Plan an experiment using Newton's second law, investigating the effect of force AND mass on acceleration
1. Place a trolley on a ramp with a light gate and have it hold a piece of paper with a gap meaning it interrupts the light gate twice 2. Attach the trolley to a sting that goes over a pulley and is connected to a hook on the other side with masses attached 3. Record the starting distance and the total mass of the system and let go of the trolley so that the hanging mass pulls it forward 4. The light gates record the velocity of the two interruptions based on their lengths, and from that works out the acceleration 5. Repeat 3 times for each force to find an average for each, and increase the mass to increase force keeping the trolley mass constant 6. Plot a graph of acceleration against force - it should show a straight line relationship that proves F = ma
81
What are factors to consider when investigating Newton's second law?
- the weight of the hook AND masses attached to it provide the accelerating force, equal to mass of hook (m) x acceleration due to gravity (g) - the accelerating force acts on both the trolley and the masses, so you are investigating the acceleration of the whole system (the trolley + the masses) - you can adjust the independent variables to investigate different things (read the question to make sure you've altered the right things)
82
How do you investigate the effect of mass on acceleration?
Use the general idea of the investigation on Newton's second law but: 1. Add masses to the TROLLEY in regular intervals, to increase the mass of the system 2. Don't add masses to the hook as that would change the force 3. Record the average acceleration for each mass
83
How do you investigate the effect of force on acceleration
Use the general idea of the investigation on Newton's second law but: 1. Start with ALL the masses loaded on the TROLLEY, transferring the masses to the hook in regular intervals, to increase the accelerating force of the hanging masses 2. This means the mass of the whole system stays the same as you transfer the masses from one part of the system to another, but force is still increasing

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