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Eleanor Rowe Physics > Forces > Flashcards

Forces Flashcards

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1
Q

What is a vector quantity with examples

A

Has magnitude and direction

Eg force velocity displacement acceleration momentum

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2
Q

What is a scalar quantity with eg

A

Only magnitude no direction

Eg speed distance mass temperature time

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3
Q

How are vectors shown

A

As an arrow

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4
Q

What is a contact force with eg

A

When two objects have to touch for a force to act

Eg friction air resistance tension in rope normal contact force

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5
Q

What is a non contact force with eg

A

Objects don’t need to be touching for the force to act

Eg magnetic force gravitational force electrostatic force

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6
Q

How are the sun and earth attracted to each other

A

Gravitational non contact force

Equal but opposite attraction is felt

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7
Q

What is gravity

A

The force of attraction between masses

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8
Q

What are the two important effects of gravity

A

Makes everything fall towards the ground on the surface of the earth
Gives everything a weight

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9
Q

What is mass
What is it measured in
What is it’s symbol

A

The amount of matter in an object
Kg
m

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10
Q

What is weight
What is it measured in
What is it’s symbol

A

The force acting on an object due to gravity
Newton’s (N)
W

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11
Q

Is mass a force

A

No

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12
Q

True/false: mass and weight are directly proportional

A

True

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13
Q

What is the equation including gravity mass and weight

Include symbols and units

A

Weight (W) (Newton’s) = Mass (m) (Kg) x Gravitational Field strength (g) (N/kg)

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14
Q

What two forces act on a skydiver

A

Drag (air resistance) and weight

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15
Q

What is a free body diagram?

A

Diagram showing all the different forces acting on one isolated system
Length of arrows shows scale of how large each force it

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16
Q

What is a resultant force

A

The overall force on a force or object

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17
Q

Finish the sentence: when a force moves an object through a distance…

A

Energy is transferred and work is done on the object

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18
Q

What is the equation linking force work and distance with symbols and units

A

Work done (W) (J) = Force (F) (Newton’s) x Distance (s) (m)

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19
Q

What is one joule of work equal to

A

When a force of one newton causes an object to move one meter
1J=1Nm

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20
Q

What is elastically deformation

A

What an object can’t go back to its original shape and length after the force has been removed

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21
Q

What is inelastically deformation

A

The object doesn’t return to its original shape and length after the force has been removed

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22
Q

What happens when work is don’t to compress a spring

What happens if the object is inelastically deformed

A

Energy is transferred to the elastic potential energy store of the object
All the energy is in elastically deformation
Only some is in inelastically deformation

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23
Q

What is the equation that links spring constant force and extension with symbols and units

A

Force (F) Newton) = spring constant (k) (N/m) x Extension (e) (m)

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24
Q

Does a stiffer spring have a greater or lower spring constant

A

Greater

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25
Q

How is the limit for the amount of force applied to extend a spring shown on a graph and what is this called

A

The graph starts to curve showing force and extension are no longer proportional
Called the limit of proportionality

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26
Q

Practical method for investigating link between force and extension

A

Measure natural length of spring ( read at eye level)
Add mass to spring, record new length of spring
Repeat process until enough measurements
Plot a graph
Will only start to curve if exceed limit of proportionality

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27
Q

What is the equation for elastic potential energy with units and symbols

A

Elastic potential energy (E) (J) = 0.5 x spring constant (k) (N/m) x extension^2 (e) (m)

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28
Q

What is a moment

A

The turning effect of a force

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29
Q

What is the equation for moments with symbols and units

A

Moment (M) (Nm) = Force (F) (N) x distance (m)

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30
Q

What is the distance in the moment equation

A

The perpendicular distance from the pivot to the line of action of the force

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31
Q

How do levers make it easier to do work

A

They increase the distance from the pivot meaning less force is needed to get the same moment

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32
Q

What are gears

A

Circular disks with teeth around the edges

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33
Q

How do gears work

A

Their teeth interlock so that turning one causes another to turn in the opposite direction
Used to transmit the rotational effect of a force from one place to another

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34
Q

True or false a smaller gear will turn slower than a large gear

A

False a large gear turns slower

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35
Q

How will a force transmitted to a larger gear cause a bigger moment

A

The distance to the pivot is bigger

36
Q

How do you calculate the pressure at the surface of a fluid

Equation with symbols and units

A

Pressure (p) (Pa- pascals) = Force Normal to a surface (N) / Area of that surface (m^2)

37
Q

How does fluid exert a pressure

A

The particles exert a force on the object they collide with

38
Q

What does pressure in a liquid depend on

A

Density - more dense it is , more particles in a certain space, more collisions = higher pressure
Depth- number of particles above that point increases, weight of this adds to pressure felt at that point = higher pressure

39
Q

How do you calculate pressure at a certain depth due to the column on liquid above
Equation with symbols and units

A

Pressure (p) (Pa) = Height of Columbia of liquid (m) x gravitational field strength (N/kg) x density of liquid (kg/m^3)

40
Q

How is upthrust formed when an object is in fluid

A

Pressure increases with depth, so there is more pressure at the bottom of the object than at the top, this causes a resultant force called upthrust

41
Q

What is upthrust equal to when an object is in fluid

A

The upthrust is equal to the weight of the fluid that has been displaced by the object

42
Q

What happens is the fluid an object is placed in is denser than the object

A

The fluid it displaces equals in weight to the object so it floats

43
Q

What happens is the object is denser than the fluid it is placed in

A

It is unable to displace enough water to equal its weight

Meaning weight is larger than upthrust so it sinks

44
Q

How do submarines use upthrust to work

A

To sink large tanks are filled with water to increase its weight to be more than the upthrust
To ride the tanks are filled with air to reduce the weight so it is less than the upthrust

45
Q

How is atmospheric pressure created at the surface

A

By air molecules colliding with the surface

46
Q

How does atmospheric pressure decrease with increased altitude

A

The atmosphere gets less dense to there are fewer air molecules that are able to collide with the surface
There are also fewer air molecules above a surface as the height increases so pressure is reduced

47
Q

What is displacement

A

Measures the distance and direction in a straight line from a starting point to ending point

48
Q

What is the equation for time speed and distance with symbols and units

A

Distance (s) (m) = speed (v) (m/s)x time (t) (s)

49
Q

What are the typical speeds for walking running cycling a car a train and a plane

A 
Walking 1.5m/s
Running 3m/s
Cycling 6m/s
Car 25m/s
Train 55m/s
Plans 250m/s
50
Q

What is acceleration

A

How quickly you’re speeding up

51
Q

What is the equation for acceleration with symbols and units

A

Acceleration (a) (m/s^2) = change in velocity (m/s) / time (s)

52
Q

What is another name for uniform acceleration

A

Constant acceleration

53
Q

What is acceleration due to gravity as a value

A

9.8 m/s^2

54
Q

What is the equation for uniform acceleration and what does each part mean

A

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

v= final velocity
u = initial velocity 
a= acceleration 
s = distance
55
Q

On a distance time graph what does the gradient equal

A

The speed

56
Q

What do flat sections mean in a distance time graph

A

The object is stationary

57
Q

What do curves mean in a distance time graph

A

Acceleration or deceleration

58
Q

What does the gradient mean in a velocity time graph

A

The acceleration

59
Q

What do flat sections mean in velocity time graphs

A

Steady speed

60
Q

What do curves mean in velocity time graphs

A

Changing acceleration

61
Q

What does the area under and velocity time graph mean

A

The distance travelled

62
Q

What is friction

A

A force that always acts in the opposite direction to movement

63
Q

What is friction called through a fluid

A

Drag

64
Q

What happens to drag when speed increases

How can this be stopped

A

It increases

Keep the object streamlined allowing fluid to flow easily across it

65
Q

How do parachutes use drag

A

They increase their SA to make it difficult for fluid to flow across it, slowing them down

66
Q

How does an object falling through fluid reach a terminal velocity

A

When it first sets off, the force of gravity is much more than the frictional force slowing it down so it accelerates
As speed increases, friction builds up
This gradually reduces acceleration until the frictional force is equal to the accelerating force
At this point there is no resultant force and the object has reached its max speed or terminal velocity

67
Q

What does terminal velocity depend on

A

Shape and area

68
Q

What is a good example for showing that shape and area effect terminal velocity

A

A human skydiver with no parachute will have less air resistance meaning their terminal velocity is dangerously higher
A human skydiver with a parachute will have more air resistance meaning their terminal velocity is at a lower safer rate

69
Q

What is Newton’s first law

A

A resultant force is needed to make something start moving speed up or slow down

70
Q

What is Newton’s second law

A

Acceleration is proportional to the resultant force

71
Q

What formula shows Newton’s second law with symbols and units

A

Resultant Force (F) = mass (m) (kg) x acceleration (a) (m/s^2)

72
Q

What is inertia

A

The tendency for motion to remain unchanged

73
Q

Will something with a higher or lower mass have a greater inertia

A

Higher

74
Q

What is Newton’s third law

A

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

75
Q

Method for practical to investigate how mass and force affect acceleration

A

Set up trolly holding card with gap in middle to interior light gate twice ( will calculate velocity)
Connect trolly to string through pulley and add hook on end to hang mass on
Masses added provide accelerating force
Mark starting line so trolley always travels same distance
Release trolley and record acceleration
Repeat by adding masses

76
Q

What is the equation for stopping distance

A

Thinking distance + braking distance

77
Q

What factors affect stopping distance

A

Speed, reaction time, weather, brake and tire condition

78
Q

How do car brakes work

A 
Brake pads press onto wheels 
Causes friction 
Causes work to be done 
Transfers energy from kinetic stores in wheels to thermal stores in brakes 
Causes increase in temperature
79
Q

How to measure reaction times

A

Ruler drop test

80
Q

How does speed affect braking distance

A

As speed doubles, kinetic energy increases 4 fouls (2^2), so the braking distance also increases 4 fold

81
Q

What is the equation for momentum with symbols and units

A

Momentum (p) (kg m/s) = mass (kg) x velocity (m/s)

82
Q

What happens to momentum in a closed system

A

Momentum before event is the same as after the event

83
Q

What does a larger farce mean in terms of change in momentum

A

A faster change in momentum

84
Q

How is a fast change in momentum dangerous in a car crash

A

The forces on the body will be very large and more likely to cause injury

85
Q

Why do cars have safety features

A

Designed to slow people down over a longer time when they have a crash
The longer it takes for a change in momentum the smaller the force felt, meaning injuries are less severe

86
Q

What safety features do cars have and what do they do

A

Crumple zones increase time taken for car to stop
Seat belts stretch slightly increase time sod wearer to stop
Air bags inflate and compressed air slows you down more gradually than hitting head on dashboard

Eleanor Rowe Physics (11 decks)

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