A2 PE Mechanics of Movement Flashcards
What is a scalar?
A quantity which only has a magnitude (size)
Speed, distance and mass are scalar quantities.
Linear motion is…
Movement of a body in a straight line where all parts are moving in the same direction at the same speed.
What is a vector?
A quantity that has both a direction and a magnitude (size).
Velocity, acceleration, momentum are all vectors.
It is demonstrated by an arrow which points in the direction of travel and is a length that represents the size of the force.
Speed =
Distance/time
Units are ms
Velocity =
Displacement / time (units are ms)
The amount of ground covered during motion is …
Distance (units are m)
How would you calculate displacement?
Straight line length from starting point to finishing point. (Units are m)
Acceleration =
Change in velocity/time
Vf-Vi/ time
(Units are ms)
Force =
Mass x acceleration.
E.g Weight = mass x gravity
Momentum =
Mass x velocity (units are kgms)
Impulse =
Force x time (units are ft)
When an athlete is RUNNING, the curve you would draw on an impulse graph always starts below the line, true or false?
True - this is the negative force applied when the sprinter lands on the track.
When a performer is leaving the blocks the force is totally above the line - they haven’t landed on the track yet.
When drawing an impulse graph for a sprinter who is moving at constant velocity, what would the graph look like?
A symmetrical ‘S’ shape where the negative force below the x axis is the same size and shape as the positive force above the x axis.
Name Newton’s first law, explain it and give and example.
INERTIA
A body continues in a state of rest or constant velocity unless acted upon by an external force.
E.g a swimmer will stay on the blocks until they contract their muscles to apply a force.
Name Newton’s second law, describe it and give an example.
ACCELERATION (force = mass x acceleration)
When a force acts on an object, the rate of change of velocity experienced by the object is proportional to the size of the force and travels in the direction the force is applied.
E.g the force used by a sprinter pushing off the starting blocks is equal to the force they will accelerate with in the opposite direction
Name Newton’s third law, describe it and give an example.
ACTION AND REACTION
For every action there is an equal and opposite reaction (ground reaction force)
E.g if a high jumper applies a force into the ground they will receive and equal and opposite force to allow them to jump into the air.
Forces are any push or pull which cause a change in velocity, what four things can forces do?
- Cause a body to move
- Cause a body to accelerate and decelerate
- Cause a body to change direction
- Cause a body to change shape
Give 3 examples of horizontal forces
Friction
Air resistance
Drag
Give three examples of vertical forces.
Gravity (9.8ms)
Weight force (mass x gravity)
Ground reaction force (from Newton’s 3rd law)
What is the name of the trajectory of an object in flight?
Parabola
What vertical force acts on a projectile while it is in the air?
Gravity
Which component of a parabola does gravity affect?
The vertical component - it causes the object to accelerate downwards when it is in flight. This causes the symmetrical ‘inverted U’ shape of the parabola.
What effect does air resistance have on a projectile like a person doing the long jump?
Very little as the mass of the performer is large.
It would affect the horizontal component, but it’s effect is considered to be ‘negligible’.
Give 3 factors that affect horizontal displacement of a projectile (how far the projectile travels)
Height of release
Velocity / speed of release
Angle of release
The horizontal component of a projectile like a shot put stays the same throughout flight, true or false?
True, the ‘speed’ of release will determine the horizontal component (momentum = mass x velocity).
The shot would continue to move with constant velocity until another force acts upon it (Newton’s first law)
What is angular momentum?
Angular velocity x moment of inertia
It remains constant when a rotating object is in flight
What is angular velocity?
The rate at which an object or body spins (speed of spin)
What is the moment of inertia?
Distribution of mass from the axis of rotation;
As it increases, angular velocity decreases (slower spin)
As it decreases, angular velocity increases (faster spin)
How does the mass of an object affect moment of inertia?
The greater the mass the greater the moment of inertia.
A bowling ball has a higher moment of inertia than a volleyball so will require more force to roll it along the ground.
How can a performer use their moment of inertia to increase or decrease their angular velocity (speed of rotation)?
Speed up= decrease their moment of inertia- tucking limbs
Slow down= increase their moment of inertia- extending limbs
Are moment of inertial and angular velocity A) directly proportional or B) inversely proportional?
B) inversely proportional. As one increases the other decreases.
As the rate of spin (angular velocity) of a body INCREASES, moment of inertia (distribution of mass from axis of rotation) has to DECREASE.
