Biomechanical principles Flashcards
1
Q
What are Newton’s laws of motion, how are they applied?
A
- First law, law of inertia:
- A body continues in a state of rest unless acted upon by an external force
- E.g. a golf ball will remain still unless the force applied by a golf club makes it move
- E.g. a golf ball will will continue to move at a constant velocity unless a force acts on it to slow it down, such as wind resistance or gravity - Second law, law of acceleration:
- A body’s rate of change of momentum is proportional to the size of the force applied and acts in the same direction as force applied
- E.g. when a golf ball is struck by a golf club, the velocity of the ball is proportional to the size of the force acted on it by the club - Third law, law of reaction:
- For every action there is an equal and opposite reaction
- E.g. if a tennis players hits a ball, the racquet exerts a force on the ball and the ball exerts a am equal and opposite force in the racquet. The racquet exerts the action force and the ball exerts reaction force.
- E.g. if the tennis ball then hits the floor, it exerts a force on the floor and the floor exerts an equal and opposite force on the ball.
2
Q
What is velocity, equation and unit?
A
- Velocity is the rate of change of displacement
- Velocity = displacement/time taken
- m/s
3
Q
What is momentum, equation and unit?
A
- Momentum is the quantity of motion possessed by a moving body
- Momentum = mass x velocity
- kg m/s
4
Q
What is acceleration, equation and unit?
A
- Acceleration is the rate of change of velocity
- Acceleration = (final velocity - initial velocity)/time taken
- m/s/s
5
Q
What is force, equation and unit?
A
- Force is a push or pull that alters the state of motion of a body
- Force = mass x acceleration
- N
6
Q
What are the 2 types of force?
A
- External force, which comes from outside of the body
2. Internal force, which is generated by skeletal muscle.
7
Q
What are the effects of force?
A
- Create motion
- Accelerate a body
- Decelerate a body
- Change the direction of a body
- Change the shape of the body.
8
Q
What is net force?
A
- Net force is the sum of all forces acting on the body
- If net force = 0, there is no change in motion as forces are balanced
- If net force is present, there is a change in motion as the forces are unbalanced. This occurs when two forces are unequal in size and opposite in direction.
9
Q
What are the external forces acting on the body, equation and unit?
A
Vertical forces:
- Weight,
- The gravitational pull that the earth exerts on a body
- Weight = mass x acceleration
- N - Reaction,
- The equal and opposite force exerted by a body in response to the action force placed upon it
Horizontal forces:
- Friction,
- The force that opposes the motion of two surfaces in contact
- N - Air resistance,
- The force that opposes motion through the air
- N.
10
Q
What are the factors affecting friction, examples?
A
- Roughness of the ground surface e.g. athletes run on rough, rubberised tracks
- Roughness of the contact surface e.g. athletes wear spiked shoes
- Temperature e.g. F1 drivers have a warm-up lap, as friction is increased with higher tyre temperatures
- Mass e.g. shot putters have a high mass, so due to Newton’s third law, this creates an equal and opposite high reaction force, allowing greater friction in throwing circle and preventing over-rotation.
11
Q
What are the factors affecting air resistance, examples?
A
- Velocity e.g. the greater the velocity of a cyclist, the greater the force of air resistance opposing their motion
- Shape e.g. most cyclists wear a tear-drop shaped helmet to minimise air resistance, known as streamlining
- Front cross-sectional area e.g. the low crouched position of a downward skier reduces air resistance
- Smoothness of surface e.g. lycra suits reduce air resistance.
12
Q
What is the origin and direction of the arrows representing vertical forces in a free body diagram? Relationship between the forces?
A
- Weight arrow originates from the centre of mass, extends vertically downwards
- Reaction arrow originates from the point of contact extending vertically upwards
- If weight=reaction, net force is 0 so forces are balanced therefore body will remain at rest
E.g. basketballer preparing to take a free throw, or travelling in constant vertical velocity - If reaction>weight, net force is positive
- If forces are unbalanced, acceleration in an upward direction will occur
E.g. basketballer leaving ground in the take-off phase of a layup.
13
Q
What is the origin and direction of the arrows representing horizontal forces in a free body diagram? Relationship between the forces?
A
- Friction arrow originates from the point of contact and usually extends horizontally in the same direction as motion
- Air resistance arrow originates from the centre of mass and extends horizontally against the direction of motion
- If friction=air resistance, net force is 0 so forces are balanced therefore body will remain at rest
E.g. sprint cyclist travelling in constant velocity who has reach maximum velocity is in constant velocity - If friction>air resistance, net force is positive, so forces are unbalanced and acceleration in a forward direction
E.g. sprint cyclist accelerating away from starting line - If air resistance>friction, net force is negative, so forces are unbalanced and horizontal deceleration will occur
E.g. sprint cyclist crossing the finish line sitting up and decelerating.
14
Q
What is centre of mass?
A
- Centre of mass is the point in which an object is balanced in all directions
- The point where the weight of the body tends to be concentrated.
15
Q
What is stability?
A
- Stability is the ability to move and resist motion at rest
- It is also the ability to withstand a force applied and return to original position without damage.
