Biomechanics Flashcards
What is the definition of biomechanics?
the study of motion and the effect of forces relative to the body
Define Newton’s 1st Law of Motion and explain how this applies to golf
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.
Define Newton’s 2nd Law of Motion and explain how this applied to running.
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.
Define Newton’s 3rd Law of Motion and explain how this applies to swimming
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.
What is the formula for linear momentum?
Momentum= mass x velocity
Explain the concept of a perfectly elastic collision
a collision where energy is fully transferred and no energy is lost via sound and heat. COR= 1
Explain the concept of a imperfectly elastic collision
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.
Explain the concept of a perfectly inelastic collision
there is no bouncer and therefore linear momentum is not conserved. COR= 0
Law of conservation of linear momentum
In the case where the collision between 2 objects is perfectly elastic, the total momentum of the system remains constant.
Define impulse
How much force is produced over a time interval and the change in momentum. Impulse = Force x Time
What is the impulse- momentum relationship?
Impulse is the change in momentum. Momentum is increased by increasing impulse.
What is the coefficient of resititution?
The ratio of the velocity of the ball after impact compared with the velocity of the ball before impact.
List the factors that affect the coefficient of restitution and state the effect it has
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.
Define Angular momentum
the amount of motion a rotating object has. Angular momentum = Moment of Inertia x Angular Velocity
Explain Moment of Inertia
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.
Explain Torque
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.
What is a first class lever?
A lever where the axis/ fulcrum is located in the middle of the force/ effort and resistance/ load.
- Examples: seesaw
What is a second class lever?
A lever where the load/ resistance is in the middle.
- Examples: push up, wheelbarrow
What is a third class lever?
A lever where force/ effort is in the middle.
- Example: bicep curl
What is laminar flow?
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.
What is turbulent flow?
When the nice, neat pattern of airflow breaks down and no longer occurs in parallel sheets, rather independent and largely random.
List the factors that affect boundary layer separation
- 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.
List 5 factors that affect drag
- speed of moving object
- surface roughness
- cross sectional area
- shape
- air density
What is surface drag? And what are ways in which it can be reduced?
The friction produced between fluid and surface of a moving object.
- It can be reduced by wearing tight clothing and shaving.
What is form drag? And how can it be reduced?
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.
What is wave drag? And how can it be reduced?
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.
Define buoyancy
The upward force that keeps object afloat.
State Archimedes’ Principle
The buoyant force acting on an object is equal to the weight of the fluid displaced by the object.
Define lift
The component of force that acts perpendicular to the direction of flow.
What is Bernoulli’s principle?
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.
Explain what happens during top spin
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.
Explain what happens during back spin
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.
Explain what happens during side spin
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.
