Linear motion Flashcards
Define linear motion
Motion in a (straight or curved) line with all body parts moving at
the same speed in the same direction at the same time
How is linear motion created
A direct force which passes through the centre of mass of the body
What are distance and displacement
Distance (Scalar) – Total length of the path covered from position A
to B, measured in metres (m) e.g. the distance covered in a 400m race is 400m
Displacement (Vector) – Shortest straight-line route from start to finish, also measured in metres (m) e.g. the displacement covered in a 400m race is 0m
What is velocity and speed
Speed (scalar) – How fast you are travelling. The rate of change in distance and is measured in metres per second (m/s) Speed = distance / time e.g. Dale Schippers broke the 200m record in a time of 21.63s with an average speed of 9.25m/s.
Velocity (vector) – How fast you are going with a direction as well. The
rate of change in displacement and also measured in metres per second (m/s) Velocity = displacement / time e.g. Usain Bolt broke the 100m record in a time of 9.58s with an average velocity of 10.44m/s in one direction
What is acceleration and decellaration
Acceleration – The rate of change in velocity and is measured in metres per second per second (m/s/s) Acceleration = (final vel. – initial vel.) / time e.g. Usain Bolt broke the 100m record in a time of 9.58s, his first 20m split was 2.89s and his velocity was 6.92m/s, so his acceleration over the first 20 seconds was (6.92 – 0) / 2.89 = 2.39m/s/s
Deceleration - The rate of change in velocity is negative or there is a decrease in velocity over time
What do different lines mean on distance time graphs mean
Horizontal line: No change in position over time = stationary body
Straight line with positive gradient: Constant change in position over time = constant speed. Steeper gradient = faster speed
Curved line with decreasing gradient: Decreasing change in position over time = decreasing speed
Curved line with increasing gradient: Increasing change in position over time = Increasing speed
What does the gradient of a line on distance time graph mean
The gradient of the curve indicates the speed of the body at a particular instant and will show whether the body is at rest, travelling with constant speed, accelerating or decelerating
What do different lines mean on speed time graphs mean
Line with no gradient : constant speed The higher the horizontal line, the faster the speed
Line with positive gradient: increasing speed (acceleration), acceleration is constant if the line is straight
Line with positive but decreasing gradient. Accelerating to constant speed (as the line reaches zero gradient)
Line with negative gradient : decreasing speed (deceleration)
2 types of velocity that velocity time graphs show
Either horizontal velocity - positive velocity is in the initial direction of motion, negative velocity is once a change of direction has occurred
Vertical velocity : positive velocity is upwards, negative velocity is downwards
Velocity time graphs
Velocity time graphs describe the same motion as a speed/time graph, except they have a negative y axis. If the graph crosses the y axis, the body has changed direction
Line with increasing negative velocity: acceleration in a changed direction
Line with decreasing negative velocity: deceleration in the changed direction (to stop, if the line reaches the x axis)
