Section 1 - Forces and Motion

Question 1

compare speed and velocity

Answer 1

BOTH:
- tell you how fast you’re going
- measured in m/s (or km/s or mph)
HOWEVER
speed is just how fast you’re going but velocity must also have direction specified

objects could be travelling at a constant speed with changing velocity (object is changing direction at same speed)

Question 2

avg speed formula

Answer 2

avg speed = distance moved / time taken

Question 3

acceleration

Answer 3

how quickly velocity is changing

(could be change in speed or direction or both)

Question 4

unit acceleration

Answer 4

m/s^2 (NOT m/s that is velocity)

Question 5

acceleration formula

Answer 5

acceleration = change in velocity/ time taken

(a negative value means deceleration - slowing down)

formula only works when acceleration is constant

Question 6

final velocity formula

Answer 6

v² = u² + 2as

v = final velocity
u = initial velocity
s = distance travelled while accelerating
a = acceleration

formula only works when acceleration is constant

Question 7

distance-time graphs

Answer 7

tell you how far something has travelled

Question 8

how distance time graphs describe motion of object

Answer 8

gradient = speed of object
flat = stopped
steeper = faster
curves = represent acceleration
curve getting steeper = speeding up (increasing gradient)
levelling off curve = slowing down (decreasing gradient)
avg speed = total d/ time

Question 9

how velocity time graphs describe motion of an object

Answer 9

gradient = acceleration
flat = steady speed
steeper = greater acceleration/deceleration
uphill (/) = acceleration
downhill () = deceleration
area under any part of graph = distance travelled in that time
curve = changing acceleration
speed = read value off axis

Question 10

gravity and its effects

Answer 10

the force of attraction between all masses
effects:
1) on surface of planet it makes all things accelerate towards ground)
2) gives everything a weight
3) keeps planets moons and satellites in orbits

Question 11

weight vs mass

Answer 11

mass = amount of stuff in an object, the same anywhere in the universe
weight = caused by pull of gravity and changes in different planets when the force of gravity pulling is more or less

weight = measured in newtons using spring balance or newton meter
mass = NOT A FORCE measured in kg with a mass balance

Question 12

gravity/ weight force

Answer 12

close to planet acts straight downwards

Question 13

reaction force

Answer 13

acts perpendicular to a surface and away from it (so if surface is horizontal, the reaction force acts straight upwards)

Question 14

electrostatic force

Answer 14

force between two charged objects. direction depends on type of charge (like charges repel, opposites attract)

Question 15

thrust

Answer 15

push or pull due to an engine or rocket speeding something up

Question 16

drag/ air resistance / friction

Answer 16

slows something down

Question 17

lift

Answer 17

occurs due to an aeroplane wing

Question 18

tension

Answer 18

occurs in a rope or cable

Question 19

balanced forces examples

Answer 19

weight and reaction force (prevents it from continuously falling)

Question 20

what is friction

Answer 20

friction is the force that opposes motion

if an object has no force pushing it along it will always slow down and stop because of friction

to travel at a steady speed things always need a driving force to counteract the friction

Question 21

how can friction occur

Answer 21

1) between solid surface that are gripping (static friction)
2) between solid surfaced gripping past each other (sliding friction)
- both of these can be reduced by adding a lubricant such as oil in between. this friction can cause wear.

3) resistance or drag from fluids
- to reduce friction keep shape of object streamlined
- for a given thrust the higher the drag the lower the top speed
- in a fluid friction always increases as the speed increases

Question 22

The First Law of Motion - balanced forces

Answer 22

balanced forces mean no change in velocity, the object will stay still or carry on at a constant speed because there is zero resultant force

Question 23

Second Law of Motion - resultant force

Answer 23

means acceleration in the direction of the resultant force. Acceleration can take forms of:
- starting
- stopping
- speeding up
- slowing down
- changing direction
and on a diagram arrows will be unequal

Question 24

resultant force fromula

Answer 24

= mass x acceleration (F=ma)

• bigger force = greater acceleration/ deceleration
• bigger mass = smaller acceleration
• to get a big mass to accelerate you need a bigger force
• you must add or subtract the forces to get the overall resultant force

Question 25

vector quantity

Answer 25

have a size and direction

such as: force, velocity, acceleration, momentum…

Question 26

scalar quantity

Answer 26

have size but no direction

such as mass, temperature, time, length…

Question 27

terminal velocity process

Answer 27

• object first starts to fall, it has much more force accelerating it towards the ground than resistance slowing it down
• as velocity increases resistance builds up
• resistance force gradually reduces acceleration until eventually the resistance force is equal to the accelerating force
• at this point the object wont be able to accelerate any more, it will have reached its maximum velocity - its terminal velocity

Question 28

terminal velocity of an object depends on:

Answer 28

shape and area
- air resistance causes things to fall at different speeds, and the terminal velocity of any object is determined by its drag compared to its weight, which depends on the shape and size

Question 29

hookes law

Answer 29

extension is proportional to force

Question 30

natural length

Answer 30

the unscratched metal wire is called natural length (l)

Question 31

hookes law stops working

Answer 31

• at first hookes law is obeyed and there is a straight line relationship between force and extension
• when force becomes great enough the graph starts to curve at the elastic limit
• if you increase the force past the elastic limit the material will be permanently streched.
• materials like rubber only obey hookes law for really small extensions

Question 32

after an elastic deformation

Answer 32

a material can return to its original shape, and if it does it displays elastic behaviour
- they will do this as long as hookes law is obeyed

Question 33

stopping distance

Answer 33

thinking distance + breaking distance

Question 34

what is stopping distance

Answer 34

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

Question 35

Thinking Distance

Answer 35

distance the car travels in the time between the driver noticing the hazard and applying the breaks

affected by
- how fast your going
- your reaction time (inexperience, alcohol, drugs, old age, tiredness…)

Question 36

Breaking distance

Answer 36

distance the car travels during deceleration whilst the breaks are being applied

affected by:
- how fast your going
- the mass of your vehicle (larger mass takes longer to stop)
- quality of breaks
- quality of grip (which depends on road surface, weather and tyres)