Lesson on acceleration and force presented to 9th graders.

1. Acceleration and Force
Sec 2 and 3
Thursday 10/3/13

2. Acceleration
• The rate of change of velocity
• Speeding up
– Increasing speed/velocity = positive acceleration
• Slowing down
– Decreasing speed/velocity = negative acceleration

3. 2 ways to Change Velocity
1. moving by going faster
2. Moving by changing direction
Change in velocity = Final velocity – initial velocity

4. Calculating Acceleration
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Acceleration = a
Velocity final = VF
Velocity initial = Vi
Time = t
units = meter per second
squared (m/s2)
Change in Velocity
(Vf – Vi)
Acceleration Time
• Acceleration of gravity = 9.8 m/s2

5. Roller Coasters and acceleration

6. Practice Problems
• A ball is dropped from a cliff and has an
acceleration of 9.8 m/s2 . How long will it take
for the ball to reach a speed of 24.5 m/s?
• A sprinter leaves the starting blocks with an
acceleration of 4.5 m/s2. What is the
sprinter’s speed 2 seconds later?

7. Homework
• 10.3 – Ch 2 Reinforcement section 2

8. Friday 10.4.13
• Drop box Reinforcement sec 2
• Pick up 10.4 – Reinforcement sec 3
• Force Notes

9. Goals
• Explain how force and motion are related
• Describe Inertia
• Explain what forces are present in a car crash

10. Tug-of-War
• The photo shows one team pulling but not
very much moving. In which direction must
the other team be pulling? Why?
• If one team tugs the other over the line, what
can you assume about the pulls exerted by the
two teams?

11. Force
• Is a push or a pull
• What happens to an object when you push or
pull it?
– Transfer of energy from one object to another object

12. 2 types of forces
• Balanced forces – two or more forces acting
on an object in opposite directions causes a
net force of zero (no movement)
• Unbalanced forces – two forces acting on an
object in the same direction (movement in the
direction of the bigger force)

13. Inertia
• The tendency of an object to resist any change
in motion
– An object in motion will stay in motion until
something stops it
– An object at rest will stay at rest until acted on
• The more mass an object has the more inertia
or the harder it is to stop once in motion
– Think of stopping a toy car with your hand and a
real car with your hand. Which one is possible?

14. Newton’s First Law of Motion
• An object in motion stays in motion and an
object at rest stays at rest until an unbalanced
force acts on it.
• Also known as the Law of Inertia
• Ex: car crashes and seat belts

15. Homework
• 10.4 Reinforcement section 3