Biomechanics

Question 1

What is the definition of biomechanics?

Answer 1

the study of motion and the effect of forces relative to the body

Question 2

Define Newton’s 1st Law of Motion and explain how this applies to golf

Answer 2

An object in motion tends to stay in motion and an object at rest tends to stay at rest unless acted upon by an unbalanced / external force.

• the golf ball will remain on the tee unless acted upon by an external force which can be force from the golf club or wind.
• the golf ball will continue to roll on the grass unless acted upon by the external force of friction.

Question 3

Define Newton’s 2nd Law of Motion and explain how this applied to running.

Answer 3

The rate of change of acceleration to a body is proportional to the force applied to it, and indirectly proportionate to the mass of the object.
- the lighter person will be able to accelerate faster than the heavier person as mass is indirectly proportionate to acceleration, thus the lower the mass, the greater the acceleration.

Question 4

Define Newton’s 3rd Law of Motion and explain how this applies to swimming

Answer 4

For every action, there is an equal and opposite reaction.
- when pushing off the swimming blocks, a person is able to accelerate faster as when force is applied to the blocks, the blocks applies an equal and opposite force onto the body which allows the swimmer to accelerate faster.

Question 5

What is the formula for linear momentum?

Answer 5

Momentum= mass x velocity

Question 6

Explain the concept of a perfectly elastic collision

Answer 6

a collision where energy is fully transferred and no energy is lost via sound and heat. COR= 1

Question 7

Explain the concept of a imperfectly elastic collision

Answer 7

the total system momentum is not conserved and some energy is lost to the collision, as exemplified by sound and heat, and change of the shape of the object.

Question 8

Explain the concept of a perfectly inelastic collision

Answer 8

there is no bouncer and therefore linear momentum is not conserved. COR= 0

Question 9

Law of conservation of linear momentum

Answer 9

In the case where the collision between 2 objects is perfectly elastic, the total momentum of the system remains constant.

Question 10

Define impulse

Answer 10

How much force is produced over a time interval and the change in momentum. Impulse = Force x Time

Question 11

What is the impulse- momentum relationship?

Answer 11

Impulse is the change in momentum. Momentum is increased by increasing impulse.

Question 12

What is the coefficient of resititution?

Answer 12

The ratio of the velocity of the ball after impact compared with the velocity of the ball before impact.

Question 13

List the factors that affect the coefficient of restitution and state the effect it has

Answer 13

Temperature. An increase in temperature results in an increase in COR.
Velocity. An increase in velocity results in an increase in COR, up until the point where the ball becomes too compressed.
Materials of interacting bodies.
Nature of striking implements. The greater impulse that can be created with the implements, the greater the COR.
Nature and condition of the ball. New balls have a higher COR than older balls as they are more elastic.

Question 14

Define Angular momentum

Answer 14

the amount of motion a rotating object has. Angular momentum = Moment of Inertia x Angular Velocity

Question 15

Explain Moment of Inertia

Answer 15

The reluctance of a body to rotate around an axis of rotation and the distribution of an object’s mass to it’s axis of rotation. Moment of inertia = mass x radius ^2. The closer the objects mass is distributed to its axis of rotation, the smaller the moment of inertia and the greater its velocity.

Question 16

Explain Torque

Answer 16

The magnitude of the turning force.

• Torque = force x perpendicular distance
• the longer the perpendicular distance, the greater the torque and the easier it is for movement to occur.
• Variables that affect torque: amount of force, angle of application of force and the length of the moment arm.

Question 17

What is a first class lever?

Answer 17

A lever where the axis/ fulcrum is located in the middle of the force/ effort and resistance/ load.
- Examples: seesaw

Question 18

What is a second class lever?

Answer 18

A lever where the load/ resistance is in the middle.

- Examples: push up, wheelbarrow

Question 19

What is a third class lever?

Answer 19

A lever where force/ effort is in the middle.

- Example: bicep curl

Question 20

What is laminar flow?

Answer 20

The fluid which occurs in “sheets” parallel to each other. Boundary layer separation takes place earlier due to the large pressure differential between the front and rear of the ball.

Question 21

What is turbulent flow?

Answer 21

When the nice, neat pattern of airflow breaks down and no longer occurs in parallel sheets, rather independent and largely random.

Question 22

List the factors that affect boundary layer separation

Answer 22

• Velocity of the object. The lower the velocity, the later the boundary layer separation.
• Surface roughness. Rough surface creates turbulent boundary layer, reducing effect of fluid resistance.

Question 23

List 5 factors that affect drag

Answer 23

• speed of moving object
• surface roughness
• cross sectional area
• shape
• air density

Question 24

What is surface drag? And what are ways in which it can be reduced?

Answer 24

The friction produced between fluid and surface of a moving object.
- It can be reduced by wearing tight clothing and shaving.

Question 25

What is form drag? And how can it be reduced?

Answer 25

Resistance created by the pressure differential between the front and back of an object moving through a fluid. - It can be reduced by decreasing the body's cross sectional area.

Question 26

What is wave drag? And how can it be reduced?

Answer 26

Resistance formed by the creation of waves at point where air and water interact. - It can be reduced by moving in a streamlined motion and swimming underwater.

Question 27

Define buoyancy

Answer 27

The upward force that keeps object afloat.

Question 28

State Archimedes' Principle

Answer 28

The buoyant force acting on an object is equal to the weight of the fluid displaced by the object.

Question 29

Define lift

Answer 29

The component of force that acts perpendicular to the direction of flow.

Question 30

What is Bernoulli's principle?

Answer 30

An increase in the velocity of fluid occurs simultaneously with a decrease in pressure. An object will tend to move towards an area of low pressure.

Question 31

Explain what happens during top spin

Answer 31

As the boundary layer rotates with the ball, the particles on top of the ball decrease in speed as they crash into the particles of oncoming air. The particles under the ball increase in speed as they are moving in the same direction as the general airflow. Therefore, the magnus force pulls a ball with top spin down towards the area of low pressure.

Question 32

Explain what happens during back spin

Answer 32

As the boundary layer rotates with the ball, the particles on the bottom of the ball decrease in speed as they crash into the particles of oncoming air. Simultaneously, the particles on the top of the ball increase in speed as they are moving in the direction of oncoming airflow. Since low pressure is created by a fast velocity, the magnus force pulls the ball and trajectory upwards.

Question 33

Explain what happens during side spin

Answer 33

At one side of the ball, the boundary layer is moving in an opposite direction to moving air. The resulting collision results in deceleration and an area of high pressure on this side. On the other side, the opposite occurs. Eg: A ball struck with an eccentric force on the left side of the ball will deviate its flight path to the right.