3.2.2.3 Linear motion part 2 Flashcards
acceleration
rate of change of velocity
change in velocity divided by time
increase in velocity = +ve acceleration
decrease in velocity = -ve acceleration
velocity
rate of change of displacement
displacement
shortest route in straight line between start and finish
weight
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
scalar
quantities that just have size
momentum
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)
conservation of momentum
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
force
changes body state of motion
e.g. gravity, ground reaction force
2 types of forces in linear motion
internal (applied when skeletal muscles contract)
external (comes from outside the body) e.g. friction, weight, air resistance
vertical forces
weight
reaction force
horizontal forces
frictional force
air resistance
e.g swimming
water driven backwards by the swimmer
water thrust forwards on swimmer (reaction)
friction
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
reaction forces
sprinter pushes back and down on the ground
ground pushes upwards and forwards on sprinter
static friction
no movement between surfaces
friction acts in opposite direction of travel
sliding friction
surfaces moving/sliding over one another
friction acts in opposite direction to travel
e.g. skiing
weight COM=accelerationacting downwards
larger skiing = less friction = more weight distributed across a larger area = less force
friction depends on:
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
air resistance (drag)
objects moving throughfluids (gas/liquids)
oppose motion
less than friction effects and weight = low values compare forces = streamlining less important
4 factors affecting air resistance
- velocity
- shape
- surface characteristics
- cross sectional area of moving body
streamlining effect & 4 examples
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)
cyclist and air resistance example
cyclist faster = increase air resistance
crouches = decrease forward cross section
helmet = minimise turbulent flow
clothing/wheel profile = assist streamlining
shot-put example
air resistance is less as not as much as weight (air resistance much less than weight)
weight = less effect air resistance = greater
high jumper take off
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
impulse
change in momentum
Ft =mv - mu
measured in newton seconds (Ns)
increasing impulse
- bigger force
- 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
force time graphs
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
sprinting force time graphs
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
