Define the centre of mass
Average position of all the parts of the body
What are the 4 factors improving stability?
- Lower height of centre of mass
- Wider area of base of support
- Position of line of gravity - vertical in line with body
- Larger body mass over base of support
Name all the scalars and vectors
Scalars - mass, speed, distance
Vectors - displacement, velocity, weight, acceleration, momentum
What are the 4 equations with units?
- Speed (ms-1) = distance/time
- Velocity = displacement/time
- Acceleration (ms-2) = change in velocity/time
- Momentum (Kgms-1) = mass x velocity
- Impulse (Ns) = force x time
Does the start or end of a 100m race have more force at the start?
- The end has a larger (negative) force at the start
Define Newton’s first law of angular motion
A body will remain at rest or continue to turn about its axis at constant angular momentum unless a large enough force is acted upon it
Newton’s second Law of angular motion - define
The angular acceleration of a body is proportional to the torque causing it and takes place in the direction in which the torque acts
Newton’s third law of angular motion - define
For every torque exerted by one body on another, there is an equal and opposite torque exerted by the second on the first
Define angular momentum, and give the equation
- The quantity of angular motion possessed by a body
- Moment of inertia x angular velocity
What factors increase the moment of inertia?
- The bigger the mass, the bigger the moment of inertia
- The further the mass of an object is spread around the axis of rotation
What is meant by a closed system, and what are the examples of it?
- No external eccentric forces are acting upon it, so the momentum will remain constant
- This is known as the conservation of angular momentum
- Ice skater and diving somersault
- A dance pirouette isn’t closed because there is friction between shoes and ground
What 3 factors increase horizontal displacement?
- Faster speed of release
- Higher height of release
- Angle of release:
below 45 degrees if above landing area
above 45 degrees if below
45 degrees if same
What are the factors affecting whether an object will have a parabolic flight path?
- Weight - the heavier the object, the less it is affected by air resistance, and therefore the more parabolic its flight path
- Air resistance - the greater the air resistance, the less parabolic the flight path is. The faster an object is travelling, the more it is affected by air resistance
Define surface and form drag
- Surface drag - friction between the surface and fluid environment (air or water)
- Form drag - The impact of the fluid environment on the object. eg bigger flat objects produce more form drag
What factors can reduce drag?
- A lower velocity
- A smaller cross sectional area
- The shape and characteristics (eg materials) of the surface - streamlining the shape of something by reducing the size of the leading edge or slip streaming another performer can reduce form drag
What does the Bernoulli Principle state?
- States that air molecules exert less pressure the faster they travel
- Air pressure and air speed are inversely proportional
Apply the Bernoulli Principle to a Discus
- Important to maximise distance by generating upwards lift (greater horizontal displacement) and reducing the impact of drag forces
- Form drag can be decreased by reducing the cross sectional area of the discus depending on the angle of attack
- If angle of attack is too high, cross sectional area will increase, as so too will form drag, reducing horizontal displacement
- If the angle of attack is too low, the cross sectional area will be low, as will form drag, but not enough lift force would be generated, reducing horizontal displacement
- To generate upwards lift force while discus is in the air, angle of attack should be 25 to 40 degrees
- That way, air travels a greater distance over the top of the discus, resulting in higher air speed and low air pressure
- Can’t really impact surface drag/shape/characteristics for discus
Apply the Bernoulli principle to a cyclist
- Streamlined position to reduce form drag
- Wear specialist equipment such as lycra suits and specially designed helmets which reduce form drag because of cross sectional area, and also surface drag as they’re made from smooth materials
- Positioning of cyclists means air travelling under them has more distance to travel than over
- Higher pressure over them pushing them down, giving them more friction with the ground, enabling them to go round corners with more control
- Newton’s third law applies here as the harder the cyclist can push down on the ground, the greater the reaction force will be and the faster they will move
