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CIE

P1. Motion

P1-1:  Define speed and calculate speed from (total distance / 
            total time)

P1-3  Plot and interpret a speed/time graph and a distance/time  graph

P1-4  Recognise from the shape of a speed/time graph when a 
          body is:
          • at rest
          • moving with constant speed
          • moving with changing speed   

Motion graph summary

On a displacement-time graph …

• slope equals velocity.
• the "y" intercept equals the initial displacement.
• straight lines imply constant velocity.
• curved lines imply acceleration.
• an object undergoing constant acceleration traces a portion of a parabola.
• average velocity is the slope of the straight line connecting the endpoints of a curve.
• instantaneous velocity is the slope of the line tangent to a curve at any point.
• positive slope implies motion in the positive direction.
• negative slope implies motion in the negative direction.
• zero slope implies a state of rest.
• The area under the curve is meaningless

On a velocity(speed)-time graph …

• slope equals acceleration.
• the"y" intercept equals the initial velocity.
• straight lines imply uniform acceleration.
• curved lines imply non-uniform acceleration.
• an object undergoing constant acceleration traces a straight line.
• average acceleration is the slope of the straight line connecting the endpoints of a curve.
• instantaneous acceleration is the slope of the line tangent to a curve at any point.
• positive slope implies an increase in velocity in the positive direction.
• negative slope implies an increase in velocity in the negative direction.
• zero slope implies motion with constant velocity.
• the area under the curve equals the change in displacement.

 

P1-8  Demonstrate a qualitative understanding that acceleration 
           is related to changing speed.    

When velocity is changing, the word acceleration is used. Acceleration is also a vector. You speed up if the acceleration and velocity point in the same direction. You slow down (also referred to as decelerating) if the acceleration and velocity point in opposite directions. When you accelerate or decelerate, you change your velocity by a specific amount over a specific amount of time. 

P1-2:  Distinguish between speed and velocity

P1-5  Recognise linear motion for which the acceleration is 
          constant and calculate the acceleration

P1-6  Recognise motion for which the acceleration is not 
          constant

P1-7  Calculate the area under a speed/time graph to work out 
          the distance travelled for motion with constant 
          acceleration

Acceleration

In everyday language we use 'accelerate' to mean speeding up and 'decelerate' to mean slowing down. In scientific terms 'acceleration' is the rate at which something changes its speed - faster or slower.

Acceleration depends on two things:

• How much the speed changes
• How much time the change in speed takes

Calculating acceleration

acceleration = change in speed / time taken

Example- A bus accelerates from 5 m/s to 25 m/s in 10s

To calculate its acceleration, first find the change in speed.

This is 25m/s - 5m/s = 20m/s

Acceleration = 20m/s ÷ 10s = 2m/s2

Revision

Speed, velocity & acceleration Revision Site