9.1 - linear motion

linear motion

• movement of a body in a straight or curved line, where all parts move the same distance, in the same direction over the same time

example of linear motion

•  a water skier on a flat lake being pulled at a constant speed will travel in linear motion as all parts of their body will travel the same direction over the same distance per unit of time

How is linear motion created

• direct force being applied directly to the body’s centre of mass

direct force

• a force applied through centre of mass resulting in linear motion

centre of mass

• the point at which the body is balanced in all directions

• it is the point at which weight appears to act

5 linear motion descriptors

1. distance

2. displacement

3. speed

4. velocity

5. acceleration/ deceleration

distance

• the total length covered from start to finish

• metres → m

• e.g

  • distance covered in an 100m sprint is 100m

displacement

• the shortest straight line route between the start and finish

• e.g

  • the displacement of an 100m sprint is 100m

  • 2 lengths of a swimming pool displacement is 0m as start and finish in the same place

speed

• the rate if change in distance

• m/s → metres per second

• calculated using:

  • speed = distance / time

velocity

• the rate of change in displacement

• m/s → metres per second

• calculated using:

  • velocity = displacement / time taken

acceleration / deceleration

• rate of change in velocity

• m/s/s → metres per second squared

• acceleration = (final vel - initial vel)/ time taken

  • pos = acceleration

  • negative = deceleration

linear motion graphs

1. distance/ time

2. speed/time

3. velocity/time

distance time graph

• a visual representation of distance travelled plotted against time taken

distance time graph: Rest

distance time graph: constant speed

distance time graph: acceleration

distance time graph: deceleration

speed / time graph

• a visual representation of the speed of motion plotted against the time taken

• gradient = acceleration of a body

  • pos grad = acceleration

  • straight = constant speed

  • neg grad = deceleration

• area underneath = distance travelled

speed / time graph : constant speed

speed / time graph : acceleration

speed / time graph : deceleration

velocity/ time graph

• a visual representation of the velocity of motion plotted against the time taken 

• gradient = acceleration of a body at rest or travelling at a constant velocity

explain the graph - somersault

• A 

  • X axis = 0 

    • Rest or stationary position 

• A-B 

  • Upward curve shows an increase in velocity 

  • Acceleration 

• B-C 

  • No change in velocity per unit of time 

  • Uniform velocity = velocity is constant at this point

explain the graph - passing between the two players

• A-B 

  • Acceleration 

  • Player A applies a force to accelerate the ball towards player B 

• B-C 

  • Deceleration 

  • Player b cushions the ball to decelerate it to a resting position at C 

• C-D 

  • Rest 

  • Player b controls the ball and prepares to return the pass 

• D-E 

  • Acceleration followed by deceleration in the opposite direction 

  • Player b applies the force to the ball, accelerating it back to player A ,who cushions the ball so decelerating it to rest