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Physics Paper 2. > First Half of Forces > Flashcards

First Half of Forces Flashcards

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1
Q

What does gravity attract?

A

All masses.

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2
Q

What are the two important effects fo gravity?

A

-On the surface of a planet it makes all things fall towards the ground. - It gives everything a weight.

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3
Q

What is mass?

A

Amount of stuff in an object. For any given object this has the same value anywhere in the universe.

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4
Q

What is weight?

A

The force acting on an object due to grabity which is the graviational force on the object. Close to Earth this force is caused by the gravitational field around the Earth

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5
Q

Where is gravitational field the strongest?

A

The closer you are to the mass causing the field and stronger for larger masses.

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6
Q

What does the weight of an object depend on?

A

Strength of the gravitational field at the location of the object, so the weight of an object changes with its location

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7
Q

What is weight measured in?

A

It is a force measured in newtons.

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8
Q

Where does force act?

A

Force acts on a single point on the object called its centre of mass a point where all mass is conentrated.

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9
Q

Where does force act on a uniform object?

A

A shape with same density throughout and is a regular shape, this will be at the centre of the object.

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10
Q

What is weight measured with?

A

Calibrates spring balance or a newtonmeter

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11
Q

What is mass not?

A

A force. Measured in kg with a mass balance

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12
Q

Give the equation for weight.

A

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

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13
Q

For earth and moon what is the gravitational field strength?

A

Earth = 9.8 N/kg Moon = 1.6 N/kg

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14
Q

What does increasing the mass of an object do to its weight?

A

It increases it. If you double the mass the weight doubles to so weight and mass are directly proportional. so W fish symbol M

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15
Q

What is drag?

A

Air resistance

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16
Q

On a free body diagram what do the arro size show?

A

Relative magnitudes of the forces and the direction shows the direction of forces acrting on the object.

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17
Q

What is a resultant force?

A

A number of forces acting at a single point you can replace them with a single force as long as the single force has same effect as the original forces all together. It is the overall force on a point or object.

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18
Q

How to find the resultant force?

A

If all forces act in same direction so are parallel the overall effect is found by adding those going in same direction and subtracting any going in the opposite direction.

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19
Q

When is energy transferred/work done on an object?

A

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

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20
Q

What must be applied to make somthing move or keep it moving if there is a frictional force?

A

A force. The thing applying the force needs to be as= source of energy like food or fuel

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21
Q

How is energy transferred from one store to another?

A

The force does work to move the object and energy is transferred

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22
Q

When you push something along a rough surface like carpet what happens?

A

You are doing work against frictional forces.

Eenrgy is being transferred to the kinetic enrergy store of the object because it starts moving.

Some energy is also being transferred tp thermal energy stores due to friction

Causes overall temperature of object to increase

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23
Q

How to find out how much work has been done?

A

W (joules) = F (N) S (distance -moved along the line of action of the force- m)

W = FS

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24
Q

Give conversion of a joule to newton metres

A

1J = 1 Nm

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25
Q

How do you draw scale drawings to fund resultant forces?

A

1= Draw the forces they have given you

2= Choose a sensible scale 1cm=1N

3= Draw resulatant force from top to bottom so it is a triangle

4= Measure new line with a ruler to find force in N

5= Use a protractor to measure direction as a bearing

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26
Q

When is an object in equilibrium?

A

When all of the forces acting on a object combine to give resultant force of 0

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27
Q

On a scale diagram what does equilibrium look like?

A

Scale forms a triangle

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28
Q

What happens when you apply a force to an object?

A

It amy stretch compress or bend

To do this you need more than one force acting on the object.

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29
Q

What happens to elastic objects?

A

They can go back to their original shape and lenghth after the force has ben removed.

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30
Q

What does it mean if an object is ineleastically deformed?

A

Doesn’t return to original shape and length after force is removed.

31
Q

How do you know when work has been done on a object?

A

When a force stretches or compresses an object and causes energy to be transferred to elastic potential store of the object.

If elastically deformed ALL this energy is transferred to objects elastic potential energy store.

32
Q

What is the extension of stretched spring directly proportional to?

A

The force applied

33
Q

Give the equation for force.

A

F = K e

F= N

K = Spring constant (N/m)

E = extension m

34
Q

What does the spring constant depend on?

A

The material that you are stretching, a stiffer spring has greater spring constant

35
Q

What does the force equation also work for?

A

Compression, where e is just the difference between the natural and compressed lengths the compression

36
Q

What is the limit of proportionality?

A

Maximum force above above which the graph curves showing the extenson is no longer proportional to force.

When the graph curves upwards that is the limit of proportionality.

37
Q

What is the force triangle?

A

F

K X E

38
Q

How to quickly experiment to check masses are a good size for investigation of link between force and extension.

A

1= Use identical spring to the one you will test load with masses one at a time until totals 5

2= measure extension each time you add another mass

3= Work out increase of spring for each of your masses

4= if any causes a bigger increase than others you need to use smaller masses as you have gone past springs limit of proportionality.

5= use smaller masses or you wont get enough measurements for your graph

39
Q

How to investigate the link between force and extension.

A

1= Meausure natural length of the spring with no load with a millimetre clamped to the stand

2= Make sure you take the reading at eye level and add a marker to bottom of the spring to make reading more accurate

3= Add a mass to spring and allow it to come to rest. Record mass and measure new length of the spring. Extension is the change in the length.

4= Repeat process until you have enough measurements no fewer than 6

5= Plot a force-extension graph of results

6= It only curves if you exceed limity of proportionality.

40
Q

How to find elastic potential energy for work done in stretching or compressing for a spring which is not past limit of proportionality?

A

E (J) = 1/2 x k (n/m) x e^2 (m)

41
Q

What can one force or several forces do to an object?

A

Rotate

42
Q

What is a moment?

A

The turning effect of a force.

43
Q

Give the equation for momentum

A

M = F X D

momentum of force = Nm

Force = N

Distance = m (perpendicular distance from the pivot to the line of action of the force)

44
Q

What causes a large moment?

A

Large force or long distance

45
Q

How to get the maximum moment?

A

Push at right angles to spanner

Pushing at any other angle means smaller distance so smaller moment.

46
Q

What makes an object balance so won’t turn?

A

If total anticlockwise moment equals total clockwise movement about a pivot it won’t turn

47
Q

What do levers do?

A

Increase distance from pivot at which the force is applied. Since M=FD this means less force is needed to get the same moment.

Levers make it easier to do work.

48
Q

What are gears?

A

Circular disks with teeth around the edges.

49
Q

How do gears work?

A

Their teeth interlock so that turning one causes other to turn in opposite direction.

They are used to transmit the rotational effect of a force from one place to another.

50
Q

Why are different sized gears used?

A

Change moment of force.

A force transmitted to larger gear will cause bigger moment as the distance to pivot is greater.

Larger gear turns slower than smaller gear.

51
Q

What are fluids?

A

Substances that can flow as their particles are able to move around. It is either liquid or gas.

52
Q

Describe movement in fluids

A

Particles move around the collide with surfaces and other particles.

Particles are light, have mass and exert force on the object they collide with.

53
Q

What is pressure?

A

Force per unit area. Particles exert force.

54
Q

What does pressure of a fluid mean?

A

Force is exerted at right angles to any surface in contact with fluid.

55
Q

How to calculate pressure at surface of fluid?

A

P = F / A

Pressure in pascals = Pa

Force = N

A = area of surface in m squared.

56
Q

What is density a measure of?

A

Compactness of a substance

For a liquid density is uniform and doesnt vary in shape or size

57
Q

What does a more dense liquid mean?

A

More particles in a certain space. So more particles are able to collide so pressure is higher.

58
Q

What happens as depth of the liquid increases?

A

Number of particles above that point increases

Weight of these particles adds to pressure felt at that point so lquid pressure increases with depth.

59
Q

How do you calculate pressure at a certain depth?

A

P = Hρg

P= pressure (pa)

h= height of column depth (m)

ρ = density of liquid kg/m^3

g= gravitational field strength (N/kg)

60
Q

What happens when an object is submerged into water?

A

Pressure of fluid exerts a force on it from every direction

61
Q

How does pressure increase?

A

With depth, so force exerted on bottom of object is larger than force acting on the top of the object.

Causes a resultant force upwards.

62
Q

What is upthrust?

A

Resultant force going upwards.

63
Q

What is upthrust equal to?

A

To weight of fluid that has been displaced (pushed out of the way) by the object.

64
Q

What happens when upthrust is equal to the object weight?

A

Force balances and object floats.

65
Q

What happens if objects weight is more than upthrust?

A

It sinks.

66
Q

What does it depend on if an object floats or sinks?

A

Its density.

67
Q

What happens if an object is less dense than fluid it is placed in?

A

It weighs less than the equivalent volume of water.

This means it displaces a volume of liquid that is equal to its weight before if is completley submerged

At this point the upthrust is equal to objects weight so it floats

68
Q

What does an object that is denser than the fluid it is placed in do?

A

Unable to displace enough fluid to equal its weight. Means that weight is always larger than upthrust so it sinks.

69
Q

How do submarines make use of upthrust?

A

To sink large tanks are filled with water to increase the weight of the submarine so that it is more than its upthrust.

To rise to surface the tanks are filled with compressed air to reduce weight so that it less than the upthrust.

70
Q

What is the athmosphere?

A

A layer of air that surrounds the Earth.

It is thin compared to the size of the Earth

71
Q

What is athmospheric pressure?

A

Created on a surface by air molecules colliding with the surface.

72
Q

As the altitude (height of Earth) increases what happens to the athmospheric pressure and why?

A
  • It decreases
  • because as altitude increases the athmosphere gets less dense so there are fewer air molecules that are able to collide with the surface.
  • Fewer air molecules above a surface as height increases. So weight o air above it contributes to athmospheric pressure whcih decreases altitude.
73
Q
A

Physics Paper 2. (4 decks)

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