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Y11 GCSE Physics > Forces And Motion > Flashcards

Forces And Motion Flashcards

(64 cards)

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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
To travel at a steady speed…
Things always need a driving force to counteract the friction
26
What three ways can friction occur?
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
Define | Static friction
Friction between solid surfaces which are grilling
28
Define sliding friction How to reduce What it can cause
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
Drag (friction)
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
Define briefly how to investigate motion (experiment)
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
Define first law of motion
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
Define second law of motion
A resultant force means acceleration If there is an unbalanced force then the object will accelerate in that direction
33
Define third law of motion
Reaction forces If object A exerts a force on object B then object B exerts an equal and opposite force on object A
34
Equation linking Resultant force Mass Acceleration
Force = mass x acceleration F M x a
35
Vector
Size and direction
36
Scalar
Only have size
37
4 examples vector quantities
Force Velocity Acceleration Momentum
38
4 examples scalar quantities
Mass Temperature Time Length
39
Example calculation to work out resultant force
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
In 3 key points describe something falling
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
What 2 things affect terminal velocity of falling objects
Shape and area
42
4 points explaining skydiver
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
Give 2 things that affect total stopping distance
Thinking distance | Braking distance
44
Define stopping distance
Distance covered in time between driver first spotting a hazard and the car coming to a complete stop
45
Stopping distance calculation
Stopping distance = thinking distance + braking distance
46
Define thinking distance | 2 things affecting it
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
Define braking distance | 4 factors affecting it
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
3 things grip on road depends on
1- road surface 2 - weather conditions 3- tyres
49
Momentum, mass, velocity equation
Momentum (kg m/s) = mass (kg) x velocity (m/s) P M x V
50
Momentum…. = …….
Momentum before = momentum after
51
What causes changes in momentum
Forces
52
Equation Force Change in momentum Time
Force (N) = change in momentum (kg m/s) / time (s) F = (mv - mu) / t V - final U - initial
53
Features in a car and what they do (safety) - 3 things
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
Define moment
The turning effect of a force
55
Moment Force Distance Equation
Moment (Nm) = Force (N) x perpendicular distance (m) between line of action and pivot
56
Where is the centre of gravity
Hangs below point of suspension
57
Define centre of gravity
Point through which the weight of an object acts
58
Principle of moments
If an object is balanced then: | Total anti-clockwise moments = total clockwise moments
59
If moments are not equal | Then principle of moments is
If the total anti-clockwise moments do not equal the total clockwise moments, there will be a resultant moment
60
Brief explanation | What is hooke’s law?
Extension is proportional to force
61
Investigation of Hooke ‘s law
``` 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
When does hooke’s law stop working
When force is great enough
63
What can a material do according to Hooke s law?
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
Describe graph with 4 points
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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