Biomechanics
Answers to Questions
1. Mass is the amount of matter that makes up an object.
Weight is the force of the Earth’s gravity on any object.
2. (i) Velocity measures the rate of positional change of an object.
(ii) When discussing velocity, it important to include information about speed and direction.
3. The velocity of an object can be changed by applying a force to it. This force may cause the object to slow down,
speed up or change direction.
4. Inertia is the tendency of an object to maintain its velocity – even if this is zero and an object is stationery.
5. (EXT) The relationship between inertia and mass is:
The greater the mass of an object, the harder it is to overcome its inertia.
6. Acceleration is a measure of how quickly velocity changes when an unbalanced force causes a body to move – this
might result is positive acceleration or negative acceleration (slowing down).
Speed is a measure of how quickly an object is travelling and is expressed/calculated as the distance travelled divided by
the time taken to travel this distance.
7. (EXT) We known that F = m x a (Force = mass x acceleration)
(i) If the same force is applied to two different objects (different masses) A = mass 5 kg will have the greatest
acceleration?
(ii) If the mass is doubled, the acceleration will be halved if the same force is applied.
8. Momentum is a measure of the amount of motion possessed by a moving body. It can also be thought of as being a
measured used to find how hard it is to stop a moving object.
Momentum = mass x velocity.
9. (i) Impulse is the amount of change in momentum a body experiences.
(ii)Impulse = force x time
(iii) (EXT) The discus spin is better than simply standing side on and releasing the discus because it allows a force to be
applied over a longer period of time – this in turn results in a greater impulse and further distances to be thrown.
10. (i) Force absorption relates to how long a force is “accepted” for. The longer a force is absorbed, the greater the
impulse is.
(ii) It better to try and “give” with the ball at point of impact rather than try to catch the ball with “rigid” or locked arms
because this increases the amount of time our hands work to slow/stop the object and creates force absorption.
11. Provide three sporting examples to clearly highlight this law which is also known as conservation of momentum.
Student responses need to clearly show the action and equal and opposite reaction e.g. Hitting any ball with a racquet,
stick or bat – at the point of impact the striking implement slows down and the ball speeds up gaining the momentum
that the striking implement has lost
12. (i) Elasticity refers to the ability of objects to “give” and then return to their original shape after contact.
ii) A tennis ball bounce more on a “rebound ace” surface such as that found at Rod Laver Arena (Melbourne) compared
to a ball bounced on the grass courts of Wimbledon because rebound ace is more elastic than grass. This means that
when the ball lands on rebound ace, less energy is lost at point of impact than on grass and hence the ball will bounce
higher.
(iii) (EXT) The greater the string tension on a racquet greater it’s elasticity. When the ball strikes a tightly strung racquet
less energy is lost compared to it striking a looser strung racquet. As a result the ball rebounds quicker from a tightly
strung racquet.
13. (i) Force summation is also known as summation of momentum and allows a performer to maximise the speed of
their body parts and also momentum at point of contact or release.
(ii) For force summation to be effective in producing maximum speed, momentum needs to move from large body parts
to small body parts.
(iii) (EXT) Many sportspeople can move body parts quickly but are not necessarily able to summate this force. This
occurs because they do not have correct timing or sequencing of their body parts.
(iv) (EXT) A follow through important after contact or release to bring about optimal performance to ensure that body
parts do not slow down at point of contact/release.
14. Accuracy and force summation are different in that accuracy requires a force to be applied in a certain direction
whereas force summation focuses on maximising the amount of force produced. Accuracy also refers to a precise and
controlled movement, which force summation does not necessarily need to be.
15. (i) Flattening the arc increases accuracy by increasing the number of times an accurate hit or release can occur at.
Without the arc being flattening, it is likely that only one (or very few) release or contact points will correspond with an
accurate outcome.
(ii) (EXT) Draw the path of a softball pitch and how the arc is flattened by the pitcher stepping forward prior to release
of the ball.
a) pitch without stepping forward/flattening the arc
b) pitch with a step forward/flattening the arc
16. (i) Friction is the amount of force that opposes a motion/movement.
(ii) Provide 3 sporting examples of where increased friction is important to successful performance
Any situation where “grip” is required – the soles of shoes (spikes, soccer/football boots, etc.); car tyres in racing;
waxing a surfboard or “gorilla grip”, etc.
(iii) Provide 3 sporting examples of where decreased friction is important to successful performance
Any situation where unrestricted movement needs to occur – a top of a billiard table; an ice skating rink; a gymnast’s
hands on the uneven bars; a swim/running suit to reduce drag; most lycra uniforms/outfits; waxing snow skis, etc.
17. All levers have 3 common parts:
The force/point of energy application
The axis/fulcrum
The resistance/load
18. There are 3 classes of levers. Draw a diagram to clearly show the three different placements of the force/effort;
axis/fulcrum and resistance/load in each class of lever.
1st Class Lever
Force
Resistance
Fulcrum/axis
2nd Class Lever
Resistance
Force
Fulcrum/axis
3rd Class lever
Force
Resistance
Fulcrum/axis
19.(i) The force arm is the distance from the force to the axis.
(ii) The resistance arm is the distance from the resistance to the axis.
(iii)The advantage of having a longer force arm than resistance arm is that it allows greater force to be exerted through
the lever with minimal/less force.
(iv) The advantage of having a longer resistance arm than force arm is that it allows a greater range of movement to
occur and potentially allows the lever to move with greatest velocity.
20. The velocity at the end of a longer lever is greater than that at the end of a shorter lever.
21. Much junior sporting equipment is made of lightweight materials such as plastic, fibreglass or aluminium and tends
to be smaller than that used by older people.
(EXT)
By reducing the mass and length of a lever you will also decrease its inertia. This will allow the piece of sporting
equipment to be rotated and manoeuvred with greater ease – this is especially important for juniors who may be
learning/practicing skills at an early stage of their development.
22. (i) Linear motion occurs when all parts of a body move the same distance and direction at the same time.
(ii) 2 sporting examples to highlight linear motion.
A skier going down a slope; a skateboarder going down a path; a rugby player being pushed backwards whilst standing
upright
23. (i) Angular motion occurs when all parts of a body rotate in the same direction at the same time around a fixed point.
(ii) 2 sporting examples to highlight angular motion.
A gymnast swinging around on the horizontal bar; a hammer throw.
24. General motion occurs when linear and angular motion occurs together.
25. (i) Torque is the action that causes a change in a body’s rotation. This results from an unbalanced force acting in a
line that does not pass through the axis of rotation.
(ii) Torque = Force x distance from the axis.
(iii) A 36-cm baseball bat will generate greater torque than a 30-cm baseball bat because the distance the force can be
applied from the axis is greater.
(iv)The 36 cm baseball bat will potentially hit the ball further because greater torque can be generated and the speed at
the end of this bat will be greater than that generated by the shorter bat.
26. (i) The moment of inertia is the tendency an object has to maintain its angular motion.
(ii) Moment of Inertia = mass x distance.
27. (i) Angular momentum is the amount of angular motion a rotating body possesses.
(ii) Angular momentum = inertia x angular velocity.
28. (EXT) Bodies rotate quicker when body parts such as the arms and legs are “tucked in” and kept close to the body,
compared to when they are extended away from the body because the tucked position results in a decreased moment of
inertia and related increase in angular velocity.
29. (a) When bodies are projected into the air the follow a curved or parabolic flight path. Factors that affect this flight
path (excluding gravity) are:
(i) velocity of release
(ii) angle of projection
(iii) height of release
(b) In most sporting situations the optimal height of release to gain maximal distance is 45 degrees.
(i) When would a height of release of 60 degrees be an advantage in a sporting situation? Provide an example.
Chipping out of a golf bunker; projecting something to a higher level than which an object is currently on; kicking a ball
in rugby so it “hangs” and increases time for team mates to try and mark it (or other examples where ball needs to stay in
the air for longer periods of time = gridiron)
(ii) When would a height of release of 30 degrees be an advantage in a sporting situation? Provide an example.
A rapid, short distance foot pass in football; when seeking a flat trajectory that decreases flight time and minimises
chance of pass being intercepted; a hard/flat pitch in softball.
30. The “Magnus effect” describes how a ball spins through the air.
(i) It is more difficult for air to pass by the side of the ball that’s spinning in the same direction as the ball is travelling.
This results in higher air pressure on this side of the ball. The ball will spin/deviate by moving from areas of high
pressure to low pressure.
(ii) What might be responsible for these pressure differences?
Different wear on the ball; one side of the ball being shinier than the other; one side of the ball being dryer than the
other, humidity in the air, etc.
31. Two factors that effect balance and stability:
(i) the size of the base of support
(ii) the position of the centre of gravity
(iii) Others: - the line of gravity; the mass of the body
32. The larger the base of support, the greater the stability of the object.
33. If the line of gravity falls outside the base of support the object becomes less stable. The closer the centre of gravity
is to being directly over the middle of the base of support the greater the stability of the object.
34. The greatest stability would be found in a: 175 cm, 90 kg footballer. This would be the case because the lower the
centre of gravity, the greater the stability of the body/object as well as the fact that the greater the mass of body, the more
stable it is.