OCR A level PE revision notes - Biomechanics

Describe Newton\'s 1st law of inertia

Antwoord: Newton’s first law states that an object will remain at rest or at a constant velocity unless acted upon by an external force. A sporting example is a golf ball on a tee at rest, the golf ball is at rest on tee until acted upon by the force of a golf club (external force). The greater the mass of the golf ball, the higher the inertia of the golf ball.

Inertia

Antwoord: Inertia is defined as the tendency of an object to resist a change in motion

Newton\'s 2nd law of acceleration

Antwoord: Newton’s second law of acceleration indicates that the larger the force applied onto a body, the higher the acceleration of that body. For example, Roger Federer applying a large force onto a tennis ball when serving means that the tennis ball will travel with higher acceleration. Thus having more pace and making the serve harder to return. However, the force of the tennis ball is dependant on the mass of the tennis ball because Force = Mass x Acceleration. A higher tennis ball at the same acceleration will result in a higher force.

Newton\'s 3rd law of action and reaction

Antwoord: Newton’s third law states that for every reaction there is an equal and opposite reaction. For example, a 100m sprinter applies a large force from his foot into the ground and the ground produces an equal and opposite reaction force back onto the 100m sprinter’s foot.

Force

Antwoord: A push or pull that alters state of motion

Describe limb kinaematics

Antwoord: Limb kinematics is the study of movement of limbs in relation to space and time, it uses body markers and multiple cameras from different angles to map body during movement. Specialist computer software can then use footage from cameras to create a 3D image of movement.

Pros of limb kinaematics

Antwoord: Data is accurate and valid for analysis. It gives good detail about technique. It can be used to analyse the technique of a specific limb.

Cons of limb kinaematics

Antwoord: Specialist equipment is very expensive and technical. Accuracy is dependant on marker placement. Some movements can’t be analysed effectively enough. The mathematical process doesn’t consider psychological and physiological makeup.

Force plates

Antwoord: Force plates are metal plates sunk into the ground electrically connected to the a computer, when an object or limb contacts the plate an electrical output is generated and converted into a graph on the computer. On the computer, size, time and direction of forces are showed. This allows reaction forces to be measured (Fx, Fy and Fx).

Pros of limb kinaematics

Antwoord: Data is immediate and accurate Useful for gait analysis of a performer

Levers

Antwoord: rigid structures that move joints

Components of a lever

Antwoord: load, effort and a fulcrum

Mechanical advantage

Antwoord: A mechanical advantage means that the effort arm is longer than the load arm, therefore larger loads can be lifted

Mechanical disadvantage

Antwoord: a mechanical disadvantage means that the load arm is longer than the effort arm. This means that heavy loads cannot be lifted.

1st class lever

Antwoord: Load - Fulcrum - Effort

Linear motion

Antwoord: movement of a body in a straight or curved line, where all body parts are moving at the same speed, direction or time. Linear motion is caused by an external force being applied through the CoM of an object.

Linear motion descriptors

Antwoord: Acceleration Velocity Speed Distance Displacement

Acceleration

Antwoord: the rate of change in velocity, measured in m/s2 Acceleration = ∆velocity/time

Velocity

Antwoord: rate of change in displacement, measured in m/s Velocity = displacement/time

Distance

Antwoord: Length of path taken from start to finish, measured in Metres Distance = Speed x time

Angular motion

Antwoord: movement of a body in a circular motion around its principle axis of rotation, angular motion is caused by an external force being applied outside the CoM of a body.

Axes of rotation

Antwoord: Transverse Frontal Longitudinal

Transverse axis

Antwoord: The transverse axis runs horizontally from side to side, a diver performing a sommersault rotates around the transverse axis.

Frontal axis

Antwoord: The frontal axis runs horizontally from front to back of the body, a gymnast performing a cartwheel will rotate around the frontal axis.

Longitudinal axis

Antwoord: The longitudinal axis runs from top to bottom of the body, a dancer performing a pirouette will rotate around the longitudinal axis.

Fluid mechanics

Antwoord: the study of forces acting on the body travelling through air or water, fluid mechanics can be used to assess the air resistance (AR) acting on a cyclist or Drag (D) on a swimmer. D and AR are slightly different, D is the force that opposes motion through water and AR is through air.

Drag

Antwoord: force that opposes motion through water

Air resistance

Antwoord: The force that opposes motion through the air

Factors of air resistance/drag

Antwoord: 1. Velocity 2. Mass 3. Surface characteristics 4. Front-cross sectional area 5. Streamlining and shape

Velocity

Antwoord: the higher the velocity, the greater the AR or D acting on a body.

Projectile motion

Antwoord: movement of a body through the air following a curved flight path through the air.

Factors affecting the horizontal distance travelled by an object

Antwoord: 1. Speed of release – greater change in momentum and acceleration if a larger force is applied. 2. Angle of release – optimum angle of release is 45o to achieve maximum horizontal distance. 3. Height of release – if release height = landing height, optimal angle of release is 45o, if release height is above landing height then optimal angle of release is below 45o. If release height is below landing height optimal angle of release is above 45o.

Shot put – free body + flight path diagram

Antwoord: 1. For the shot put, Weight (W) is the dominant force and Air Resistance (AR) is minimal therefore the flight path is parabolic, 2. parabolic meaning the flight path curve is symmetrical from release to landing.

Badminton shuttlecock

Antwoord: 1. For the Badminton shuttlecock, AR is the dominant force and W is minimal therefore a non parabolic flight path occurs, 2. a non symmetrical flight path curve shape.

Parallelogram of forces

Antwoord: 1. Draw free body diagram showing W and AR from CoM. 2. Add broken parallel lines to the W and AR to create parallelogram. 3. Draw a diagonal line from CoM to opposite corner of parallelogram, this should be labelled as the resultant force.