Dynamics and Space

Acceleration

Learning Outcomes• Acceleration of a vehicle

between two points using appropriate relationships with initial and final velocity and time of change.

• Acceleration from a velocity time graph.

Lesson 1• Define the term acceleration.• Carry out an experiment to

determine the acceleration of a trolley.

Acceleration Intro

• Have you ever heard a phrase used to describe how quick a car is?

• It can do 0 – 60 in 3 seconds.• This is an example of a cars

acceleration

AccelerationName of Car

Time to accelerate from 0-27m/s (s)

Micra 15.2Focus 12.9Corsa 19.9Ka 13.7Smart car 19.6Mondeo 13.0

Questions to consider:

1. Which car takes the shortest time to speed up to 27 m/s?

2. Which car has the fastest acceleration? Why?

3. Which car takes the longest time to speed up to 27 m/s?

4. Which car has the slowest acceleration? Why?

Acceleration• An acceleration is defined as “the

change in velocity per unit time”.

• It is the change in velocity of a body over a certain time period.

Acceleration• Acceleration, (a), can be calculated by

subtracting the initial velocity, (u), from the final velocity (v), of a body over a certain period of time, (t).

a = v – u t• Acceleration has the unit m/s2

• It is a vector quantity.

Experiment to Measure Acceleration

ResultsQuantity Value

t1, time to pass light gate 1 s

t2, time to pass light gate 2 s

t3, time to travel between light gates s

d, card length m

u, initial velocity (d / t1)

m/s

u, final velocity (d / t2)

m/s

a, acceleration(v – u / t3)

m/s2

Lesson 2• Carry out calculations for

acceleration using the equation a = v – u .

t• State that deceleration is a negative

acceleration.• Calculate acceleration from a slope

on a velocity-time graph.

Example 1

a = ?

v = 27 m/su = 0 m/st = 19.9 s

Example 2

a = 20 m/s2

v = 65 m/su = 5 m/st = ?

Example 3

a = 10 m/s2

v = ?u = 10 m/st = 5 s

Deceleration • If a moving body has a ‘negative

acceleration’ then it is decelerating.

• In other words it is slowing down.

Example

a = ?v = 0 m/su = 25 m/st = 5 s

v-t graph example• Using the v-t graph

below for the motion of a car find:

a) The initial accelerationb) The final acceleration

a) a = v – u t= 10-0

4= 2.5 m/s2

b) a = v – u t= 0-10_ (10-8)= - 5 m/s2

[note –ve sign for deceleration]

Velocity-Time Graphs

Questions on displacement and

acceleration

2011

2008

2009

2000, Qu: 21

2003 Qu: 21

2007 Qu: 21

2010 Qu: 21

SummaryAcceleration

You should now be able to do the following:

• Determine the acceleration of a vehicle between two points using a = v-u .

t

• Calculate the acceleration of a body from a slope on a velocity-time graph.