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
Acceleration
Name of
Car
Micra
Focus
Corsa
Ka
Smart car
Mondeo
Time to
accelerate from
0-27m/s (s)
15.2
12.9
19.9
13.7
19.6
13.0
Questions to consider:
1.
2.
3.
4.
Which car takes the
shortest time to
speed up to 27 m/s?
Which car has the
fastest
acceleration? Why?
Which car takes the
longest time to
speed up to 27 m/s?
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
Results
Quantity
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/s
u = 0 m/s
t = 19.9 s
Example 2
a = 20 m/s2
v = 65 m/s
u = 5 m/s
t=?
Example 3
a = 10 m/s2
v=?
u = 10 m/s
t=5s
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/s
u = 25 m/s
t=5s
v-t graph example
•
Using the v-t graph below
for the motion of a car
a)
find:
a) The initial acceleration
b) The final acceleration
b)
a =
=
=
a =
=
=
v–u
t
10-0
4
2.5 m/s2
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
Summary
Acceleration
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.