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Y11 GCSE Physics > Forces And Motion > Flashcards

Forces And Motion Flashcards

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1
Q

Define speed

A

How fast you are going with no regard to direction (scalar)

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2
Q

Define velocity

A

How fast you are going but ALSO have the direction specified (vector)

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3
Q

Equation linking
Speed
Distance
Time

A

Average speed = distance / time

S
_____
V x T

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4
Q

Define acceleration

Units

A

How quickly velocity is changing

M/s (squared)

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5
Q

Two formulas for acceleration

A

1.
Acceleration = change in velocity / time taken

Triangle: V = final velocity
(V - u). U = initial velocity
a x t

  1. (S) = (squared)

V (s) = u (s) + 2as

(No triangle)

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6
Q

Acceleration, change velocity, time calculation example

A

Accelerates: 2m/s to 6m/s in 5.6s
Find acceleration

A = change velocity / time
A = (v - u) / t
A = ( 6-2) / 5.6
A = 4 / 5.6 = 0.71 m/s (squared)
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7
Q

V squared = u squared + 2as

Calculation examples

A

Van travelling: 23m/s
Starts decelerating at 2.0 m/s squared as it heads to an area 112m away
Find speed

V (s) = u (s) + 2as
V (s) = 23 (squared) + (2 x -2.0 x 112)
V (s) = 81
V = square root 81 = 9 m/s

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8
Q 
Distance time graphs
1- tells you
2- Y axis (label)
3- x axis (label)
Tells you:
4- gradient 
5- flat
6- steep line
7- curves
8- steeper curve
9- levelling off curve
A 
1- how far something has travelled
2- distance (m)
3- time (second)
4- speed
5- stopped / stationary
6- faster
7- acceleration 
8- speeding up
9- slowing down (decreasing gradient)
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9
Q

Calculation (speed) from distance time graph

A

Speed = gradient = vertical/ horizontal

Ie: speed from 0s to 2s
Time - 2s
Distance: 20m (shown on graph)

Speed = 20 / 2 = 10m/s

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10
Q 
Velocity time graph
1-tells you
2- types of gradient
Shows you:
3- gradient
4- flat
5- steeper the graph the…
6- uphill sections
7- downhill sections
8- area under graph
9- curve
A

1 - how plotting thing’s velocity changes over time (line) ie object or person

2- positive or negative
3- acceleration
4- steady speed
5- greater the acceleration or deceleration

6- acceleration
7- deceleration
8- distance travelled
9- changing acceleration

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11
Q

Finding acceleration, speed, distance from velocity time graph calculation / equation

A

Acceleration = gradient = vertical/ horizontal
Vertical usually: velocity (m/s)
Horizontal usually: time (s)

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12
Q

Define gravity

A

Forces of attraction between all masses

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13
Q

Define mass

A

Amount of ‘stuff’ in an object

Kg

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14
Q

Define weight

Units

A

Caused by the pull of gravity

Force measured in N

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15
Q

Formula
Mass
Weight
Gravity

A 
Weight = mass x GFS
W = m x g 
Weight = N
Mass = kg
G = N
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16
Q

Name 7 different types of forces

A 
Gravity or weight
Reaction force
Electrostatic force
Thrust 
Drag
Lift
Tension
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17
Q

Force

Define gravity or weight

A

Close to a planet - this acts straight downwards

DOWN

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18
Q

Force

Reaction force

A

Acts perpendicular to a surface and away from it

If horizontal it is straight upwards

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19
Q

Forces

Electrostatic force

A

Between two charged objects

Direction depends on the type of the charge (like charges repel, opposite charges attract)

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20
Q

Forces

Thrust

A

Eg push or pull

Due to an engine or rocket speeding something up

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21
Q

Forces

Drag or air resistance or friction

A

Slowing the thing down

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22
Q

Forces

Lift

A

Ie dueto an aeroplane wing

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23
Q

Forces

Tension

A

In a rope or cable

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24
Q

Friction always….

A

Slows things down

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25
Q

To travel at a steady speed…

A

Things always need a driving force to counteract the friction

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26
Q

What three ways can friction occur?

A

1 - friction between solid surfaces which are griping
(Static friction)

2- friction between solid surfaces which are sliding past each other
(Sliding friction)

3- resistance or “drag” from fluids (liquids or gases ie air)

27
Q

Define

Static friction

A

Friction between solid surfaces which are grilling

28
Q

Define sliding friction
How to reduce
What it can cause

A

Friction between solid surfaces which are sliding past each other

Reduce: both types of friction by putting lubricant like oil or grease between the surfaces

Friction between solids can often cause wear of the two surfaces in contact

29
Q

Drag (friction)

A

Resistance or drag from fluids

Reduce;
Most important: keeping shape of object streamlined

Lorries can have “deflectors” on them to make them more streamlined and reduce drag

Roof boxes on cars spoil their streamlined shape and so slow them down

  • for a given thrust, the higher the drag the lower the top speed of the car
  • opposite is a parachute which is about high drag
  • in a fluid friction always increases as speed increases
30
Q

Define briefly how to investigate motion (experiment)

A

Motion of a toy car on a ramp

1- step up apparatus
Adjustable ramp 
Dotted line at top of ramp for car to line up
Light gate over line
Light gate at bottom of ramp
Light gate at end of ramp / runway
Toy car at dotted / start line

2 - mark line (start) in the ramp

3- measure distance between each light gate

4- let go of car just before light gate in start line

5- light gates are connected to computer. When car passes light gate beam of light is broken and time is recorded by data logging software

6- repeat several times to get average time

7- using time and distance work out average speed

31
Q

Define first law of motion

A

Balanced forces mean no change in velocity

So long as the forces on an object are all balanced then it will just stay still or else if it is already moving it will carry on at the same velocity

32
Q

Define second law of motion

A

A resultant force means acceleration

If there is an unbalanced force then the object will accelerate in that direction

33
Q

Define third law of motion

A

Reaction forces

If object A exerts a force on object B then object B exerts an equal and opposite force on object A

34
Q

Equation linking
Resultant force
Mass
Acceleration

A

Force = mass x acceleration

F
M x a

35
Q

Vector

A

Size and direction

36
Q

Scalar

A

Only have size

37
Q

4 examples vector quantities

A

Force
Velocity
Acceleration
Momentum

38
Q

4 examples scalar quantities

A

Mass
Temperature
Time
Length

39
Q

Example calculation to work out resultant force

A

Need to combine vectors

What’s resultant force of a 220N force north, a 180N force south and a 90N force south?

Start by choosing direction as the positive ie North
This means you add any forces in N and subtract forces in S direction

Resultant force = 220-180-90 = -50 N
So 50 N south

40
Q

In 3 key points describe something falling

A

1- when an object starts to fall it has much more force accelerating it than resistance slowing it down

2- as its velocity increases, resistance builds up

3- this resistance force gradually reduces the acceleration until eventually the resistance force is equal to the acceleration force. At this point, the object won’t be able to accelerate any more. It will have reached its maximum velocity or terminal velocity

41
Q

What 2 things affect terminal velocity of falling objects

A

Shape and area

42
Q

4 points explaining skydiver

A

1 - starts falling: no parachute (open) so small area and force equal to their weight pulling down

2- reached terminal velocity (resistance and weight = equal forces)

3- when parachute opens, more air resistance and still same force pulling down (larger area)

4- means terminal velocity slows down to safe speed to hit ground

43
Q

Give 2 things that affect total stopping distance

A

Thinking distance

Braking distance

44
Q

Define stopping distance

A

Distance covered in time between driver first spotting a hazard and the car coming to a complete stop

45
Q

Stopping distance calculation

A

Stopping distance = thinking distance + braking distance

46
Q

Define thinking distance

2 things affecting it

A

Distance the car travels in time between the driver noticing the hazard and applying the brakes

1- how fast your going
(Faster your going, further go)

2- reaction time
(Tiredness, alcohol, old age, distractions, inexperience)

47
Q

Define braking distance

4 factors affecting it

A

Distance the car travels during its deceleration whilst the brakes are being applied

1- how fast your going
2- mass of the vehicle (higher mass, longer to stop)
3- how good the brakes are
4- how good the grip is / friction on road

48
Q

3 things grip on road depends on

A

1- road surface
2 - weather conditions
3- tyres

49
Q

Momentum, mass, velocity equation

A

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

P
M x V

50
Q

Momentum…. = …….

A

Momentum before = momentum after

51
Q

What causes changes in momentum

A

Forces

52
Q

Equation
Force
Change in momentum
Time

A

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

F = (mv - mu) / t

V - final
U - initial

53
Q

Features in a car and what they do (safety) - 3 things

A
  1. Air bags
    Slows you down more gradually
  2. Crumple zones
    Crumple on impact, increasing time taken for car to stop
  3. Seat belts
    Stretch slightly, increasing the time taken for the wearer to stop. Reduces the forces acting on chest.
54
Q

Define moment

A

The turning effect of a force

55
Q

Moment
Force
Distance

Equation

A

Moment (Nm) = Force (N) x perpendicular distance (m) between line of action and pivot

56
Q

Where is the centre of gravity

A

Hangs below point of suspension

57
Q

Define centre of gravity

A

Point through which the weight of an object acts

58
Q

Principle of moments

A

If an object is balanced then:

Total anti-clockwise moments = total clockwise moments

59
Q

If moments are not equal

Then principle of moments is

A

If the total anti-clockwise moments do not equal the total clockwise moments, there will be a resultant moment

60
Q

Brief explanation

What is hooke’s law?

A

Extension is proportional to force

61
Q

Investigation of Hooke ‘s law

A 
1- set up apparatus
Metal pole on a weighted stand
Clamp at top of pole
Spring attached to clamp
Hanging mass off spring
Extra masses for experiment

2- measure length of spring with ruler when no load. Ruler is vertical (check with set square). Measure spring at eye level

3- add one mass at a time and allow spring to come to rest then measure new length of spring. Extension is change in length from original length.
REPEAT process until have at least 6 measurements

4- once done, repeat experiment and calculate average value for length of spring for each weight

5- plot results on graph
Force: vertical axis
Total extension: horizontal axis

6- repeat experiment using metal wire or rubber band instead of spring and compare

62
Q

When does hooke’s law stop working

A

When force is great enough

63
Q

What can a material do according to Hooke s law?

A

A material can return to its original shape after an elastic deformation

If a material returns to its original shape once forces are removed it displays elastic behaviour

64
Q

Describe graph with 4 points

A

1- limit to force you can apply for Hooke’s law to remain true.
The graph shows force against extension for typical metal wire

2- first part shows Hooke’s law being obeyed - straight line relationship between force and extension

3- when force becomes great enough the graph starts to curve

4- E: elastic limit
If increase force past the elastic limit, the material will be permanently stretched

Y11 GCSE Physics (8 decks)

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