biomechanical principles + linear motion

what is linear motion

motion in a straight or curved line with all body parts moving in the same direction at the same speed

explain how 100m sprinters and 200m sprinters use linear motion

100m sprinters travel with linear motion in a straight line during their race

200m sprinters travel with linear motion in a curved line during their race when running the bend

what is newtons first law of motion (the law of inertia)

an object will remain stationary or maintain motion in a straight line unless an external force acts upon the object

give an example of newtons first law of motion

high jumper runs in a curved line towards the bar and then changes their motion as they push off the floor and travel vertically to clear the bar

what is newtons second law of motion (law of acceleration)

force = mass x acceleration

the rate of change of momentum of a body is proportional to the force causing it, and the change takes place in the direction in which the force acts

give an example of newtons second law of motion

to provide acceleration at the seat of a race, the sprinters will have to apply a large force internally by contracting their gluteals, quadriceps and hamstrings as they drive forwards out of the starting blocks

what is newtons third law of motion (the law of action/reaction)

to every action, there is an equal and opposite reaction

give an example of newtons third law of motion

when a sprinter pushes into the starting blocks, the blocks exert an equal and opposite force onto the sprinter, allowing the sprinter to push off the blocks and accelerate

what is a scalar quantity

when measurements are described in terms of their size or magnitude

direction isn’t taken into account

what are all of the scalar quantities

speed

distance

mass

define speed

the rate of change of distance

how is speed calculated

speed = distance / time

define distance

the length of path a body follows when moving from the starting to finishing position

measured in meters

how is distance calculated

distance = speed x time

what graphs are used to show speed and distance

distance-time graphs

what does this graph state about a performer and give an example

the performer is stationary

e.g. a netballer taking a shot

what does this graph state about a performer and give an example

the performer is in a constant state of motion

e.g. long distance running

what does this graph state about a performer and give an example

the performer is accelerating

e.g. the start of a 100m sprint race

what does this graph state about a performer and give an example

the performer is decelerating

e.g. after a 100m sprinter has crossed the finish line

define mass

the quantity of matter a body possesses

measured in kg

what is the centre of mass

the point in the body at which the force of gravity can be thought to act

why do males have a higher centre of mass than women

males have broader shoulders

females have wider hips

there is more weight concentrated in these areas

what factors affect stability

• Height of the centre of mass- lowering the centre of mass will increase stability

• The position of the line of gravity- this should be central over the base of support to increase stability

• Area of the base of support- the more contact points, the larger the base of support becomes and the more stable the body becomes

• Mass of the performer- often the greater the mass, the more stability, due to increased inertia

explain the concept of centre of mass in relation to forces

centre of mass is the point on the body where gravity is thought to act upon

if a force is applied through the centre of mass this will lead to linear motion

if a force is applied outside the centre of mass this will lead to angular motion

what are the three components of a lever

fulcrum (joint)

effort (muscle/source of energy)

resistance (the weight to be moved)

what is mechanical advantage

when the effort arm is longer than the resistance arm

+ allows us to move a large load with little effort

- small range of motion

- small speed of movement

what is mechanical disadvantage

when the resistance arm is longer than the effort arm

+ large range of movement

+ fast speed of movement

- can’t lift heavy weight

draw and label a first class lever

no mechanical advantage

no mechanical disadvantage

give examples of first class levers

extension at the elbow (tricep)

neck flexion and extension

draw and label a second class lever (easy wheelbarrow)

has MA

give examples of second class levers

plantar flexion at the ankle (gastrocnemius)

draw and label a third class lever (hard wheelbarrow)

has MD

give examples of a third class lever

knee flexion and extension (quadricep and hamstring)

elbow flexion (bicep)

what are the two types of forces that can change a body’s state of motion during linear motion

internal forces

external forces

what internal forces can act upon a performer during linear motion

these forces come from within the body

when our skeletal muscles contract

what external forces can act upon a performer during linear motion

these forces come from outside the body

• air resistance

• weight (gravity)

• friction

• ground reaction force

what are the vertical and horizontal forces

horizontal- friction + air resistance

vertical- weight

what is weight and gravity

weight is a gravitational force that the earth exerts on a body, pulling it towards the centre of the earth/downwards

the greater the weight of the body, the greater the gravitational force exerted on the body is

weight is equal to the mass of the body, multiplied by the acceleration of the body due to gravity

draw a free body diagram showing the external forces

the length of the arrow reflects the magnitude/size of the force

longer = bigger force

what is friction and what are the different types of friction

friction occurs between two surfaces and acts in the opposite direction to motion

there is static friction and sliding friction

what is static friction

occurs before an object starts to slide

the force exerted on one surface by the other when there is no motion between the two surfaces

what is sliding friction

when friction acts between two surfaces that are moving relative to each other, sliding friction occurs

how does the frictional force allow us to run

when the runners foot lands on the ground the foot is stationary due to static friction

as the body moves forwards over the foot and our foot is behind, sliding friction acts forwards, stopping the foot from sliding back, allowing the runner to push off

when we stride and the foot is in front of the body, sliding friction acts backwards to stop the foot moving forwards on the surface

what factors can affect friction

The surface characteristics of the two bodies in contact e.g. running spikes- maximise friction and therefore acceleration and minimises slipping

The temperature of the two surfaces in contact e.g. curling- sweeping the ice increases the temperature which reduces the friction between stone and ice, allowing the stone to travel further

Mass of the objects that are sliding- a larger mass = greater friction

what factors affect air resistance

The velocity of the moving body- the faster the performer moves, the greater the air resistance

The cross sectional area of the moving body- the larger the cross sectional area, the greater the air resistance e.g. cyclists crouching over the handle bars

The shape and surface characteristics of a moving body- streamlined shape results in less air resistance e.g. cyclist helmets

how can athletes become more streamlined to reduce air resistance

wear lycra cycling suits

shave body hair

wear full swimsuits

wear special helmets that are aerodynamic

bike or car has an aerofoil shape

how can the effects of internal and external forces be showed on vector diagrams

explain the vector diagram for a high jumper

in the high jump the performer uses a large amount of internal muscular force generated by the gluteals, quadriceps and gastrocnemius to achieve as much vertical displacement as possible to clear the bar

the relationship between the amount of vertical force and horizontal force provided by the muscles will lead towards the vertical component

the large vertical force and small horizontal force will result in a large trajectory

explain the vector diagram for a long jumper

in the long jump the performer uses a larger internal muscular force generated by the gluteals, quadriceps and gastrocnemius to achieve as much horizontal displacement as possible

the relationship between the vertical force and horizontal force provided by the muscles will lean towards the horizontal component

the large horizontal force and small vertical force will result in the long jumper being able to jump a further distance

what is a vector quantity

measurements are described in terms of their size/magnitude and direction

what are all of the different vector quantities

weight

displacement

velocity

acceleration

momentum

what is weight

weight is a gravitational force that the earth exerts on a body, pulling it towards the centre of the earth/downwards

measured in newtons (N)

how is weight calculated

weight (N) = mass (kg) x gravity (NM)

what is displacement

the shortest distance in a straight line between the starting and finishing point

measured in meters

what is velocity

the rate of change of displacement

measured in meters per second

how do you calculate velocity

velocity (m s-1) = displacement (meters) / time (seconds)

what is acceleration

the rate of change of velocity

measured in meters per second per second

how do you calculate acceleration

acceleration (m/s/s) = change in velocity (m/s) / time (s)

what is momentum

the product of the mass and velocity of an object

measured in kg m/s)

how do you calculate momentum

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

describe what is happening to a performer in the velocity time graph

the performer is moving a constant speed/velocity

describe what is happening to the performer in this velocity time graph

what is impulse

the time it takes for a force to be applied to an object or body

measured in newton seconds (Ns)

force x time

what does an increase in impulse cause

increase in impulse → increase in change of momentum → increase in change of velocity

increase in positive impulse → acceleration

increase in negative impulse → deceleration

how can impulse be increased

impulse = force x time

we can increase force by increasing muscular force that’s applied (recruit more and bigger motor units)

we can increase the time over which a force is applied (e.g. by following through on a throw or a punch)

how can a gymnast increase their impulse to have a safe, controlled landing and reduce injury

larger negative impulse

increase time over which the force is applied by flexing their hip, knee, and dorsi flexion of the ankle

this will decrease their momentum and velocity

→ reduced impact from landing on the joints (prevent injury)

→ more control over landing because velocity + momentum are lower

what is impulse represented by on a force-time graph

an area under a force-time graph

what part of a 100m race is this force-time graph showing

the start of the race

small negative impulse- the sprinter pushes off the blocks

large positive impulse- the sprinter is accelerating

what part of a 100m race is this force-time graph showing

the middle of the race

negative and positive impulses are equal

negative impulse from when sprinters foot pushes off the ground (internal muscular force)

positive impulse from the ground reaction force (newtons third law of motion)

net impulse is 0 → sprinter is sprinting at a constant velocity

what part of a 100m race is this force-time graph showing

end of the race

small positive impulse- still going forwards

large negative impulse- decelerating