Motion for Constant Acceleration

Equations of Motion for Constant Acceleration

In this lesson the students are shown how to use a velocity-time graph to develop the equations of motion for constant acceleration.To give the students confidence, they are sometimes asked to share ideas with a partner.

We can use a velocity-time graph to find some equations that hold for a body moving in a straight line with constant acceleration.

velocity (ms-

1)

time (s)

u

v

t0

Suppose when the time is 0 . . .

At any time, t, we let the velocity be v.

the velocity is u.

Ans: The gradient gives the acceleration.

Remind your partner how to find acceleration from a velocity-time graph.

Constant acceleration means the graph is a straight line.

We can use a velocity-time graph to find some equations that hold for a body moving in a straight line with constant acceleration.

velocity (ms-

1)

time (s)

u

v

t

a = v - u t

So,

v - u

0

Suppose when the time is 0 . . . the velocity is

u.

t

From this equation we can find the value of any of the 4 quantities if we know the other 3.

At any time, t, we let the velocity be v.

Constant acceleration means the graph is a straight line.

a = v - u t

a t = v - u

v = u + a

t

Multiplying by t: u + a t = v

We usually learn the formula with v as the “subject”.

The velocity, u, at the start of the time is often called the initial velocity.