3.2.2.3 Linear motion part 2

Question 1

acceleration

Answer 1

rate of change of velocity
change in velocity divided by time
increase in velocity = +ve acceleration
decrease in velocity = -ve acceleration

Question 2

velocity

Answer 2

rate of change of displacement

Question 3

displacement

Answer 3

shortest route in straight line between start and finish

Question 4

weight

Answer 4

gravitational force exerted on object
produced by gravitational force field, force act down to earth centre
predominant force experienced by objects move freely through air

Question 5

scalar

Answer 5

quantities that just have size

Question 6

momentum

Answer 6

amount of motion a body possesses
mass x velocity

change momentum by applying a force
(sprinter pushing out of blocks and sprinter running down track)

Question 7

conservation of momentum

Answer 7

air:
no mass or velocity can be altered = momentum conserved
e.g. long jumper = gain max velocity in run up momentum no change in the air

Question 8

force

Answer 8

changes body state of motion

e.g. gravity, ground reaction force

Question 9

2 types of forces in linear motion

Answer 9

internal (applied when skeletal muscles contract)

external (comes from outside the body) e.g. friction, weight, air resistance

Question 10

vertical forces

Answer 10

weight

reaction force

Question 11

horizontal forces

Answer 11

frictional force

air resistance

Question 12

e.g swimming

Answer 12

water driven backwards by the swimmer

water thrust forwards on swimmer (reaction)

Question 13

friction

Answer 13

force that acts sideways between 2 surfaces which tend to slide past one another
-allows sports people to accelerate, slow swerve, walk, run
-grip of footwear on floor surface affects
friction acts forwards on feet of accelerating runner, runner is pushing back so friction forwards

Question 14

reaction forces

Answer 14

sprinter pushes back and down on the ground

ground pushes upwards and forwards on sprinter

Question 15

static friction

Answer 15

no movement between surfaces

friction acts in opposite direction of travel

Question 16

sliding friction

Answer 16

surfaces moving/sliding over one another

friction acts in opposite direction to travel

Question 17

e.g. skiing

Answer 17

weight COM=accelerationacting downwards

larger skiing = less friction = more weight distributed across a larger area = less force

Question 18

friction depends on:

Answer 18

force pressing surfaces together = swerving = friction acts sideways to direction of motion
-studs/spikes increase friction = swerving, accelerating and decelerating (Soft or wet surfaces)
-dry hard/solid smooth rubber = best friction
-snow and ice long slender footwear (skates/skis) = sliding friction
forward friction low, sideways friction high

Question 19

air resistance (drag)

Answer 19

objects moving throughfluids (gas/liquids)
oppose motion

less than friction effects and weight = low values compare forces = streamlining less important

Question 20

4 factors affecting air resistance

Answer 20

1. velocity
2. shape
3. surface characteristics
4. cross sectional area of moving body

Question 21

streamlining effect & 4 examples

Answer 21

shape and surface characteristics 
1-body position and shape for swimmer 
2-shape of helmets for cyclists 
3-use of lycra clothing 
4-shape of sports vehicle (car/bike)

Question 22

cyclist and air resistance example

Answer 22

cyclist faster = increase air resistance
crouches = decrease forward cross section
helmet = minimise turbulent flow
clothing/wheel profile = assist streamlining

Question 23

shot-put example

Answer 23

air resistance is less as not as much as weight (air resistance much less than weight)
weight = less effect air resistance = greater

Question 24

high jumper take off

Answer 24

weight & internal muscles down
reaction up
friction force backwards
net force = upward acceleration

GRF > = increasing the force going into ground by contraction of muscles

long jumper = horizontal force greater
high jumper = vertical force greater

Question 25

impulse

Answer 25

change in momentum
Ft =mv - mu
measured in newton seconds (Ns)

Question 26

increasing impulse

Answer 26

1. bigger force
2. apply for longer

(altered by varying force or time the force is applied)

e. g. jump higher = bend legs = apply force for longer time = larger impulse = larger change in momentum = greater final velocity = higher jump
e. g. follow through = increase contact time = increase impulse = increase final momentum = increase velocity of struck ball
e. g. gymnast bend knees when landing, change in momentum same but increase time change in momentum occurs over time increase = force exerted on gymnast less = reduce injury risk

Question 27

force time graphs

Answer 27

size of impulse = area under graph or the area between graph and the horizontal axis
positive impulse = above the axis = acceleration
negative impulse = below axis = deceleration

Question 28

sprinting force time graphs

Answer 28

deceleration -> accelerate (push off)
contact with track =-ve impulse

start:
accelerate- large +ve impulse (net = positive)
middle:
positive & negative impulse = (net = 0)= constant velocity
end:
net = negative = deceleration large -ve