1. Newton’s Second Law of Motion
How fast does it go?
Newton’s Second Law of Motion

2. Newton’s Second Law of Motion
How fast does it go?
Newton’s Second Law of Motion

3. Acceleration - Review
Acceleration makes objects speed up, slow down, or change direction.
It is caused by unbalanced forces acting on an object.

4. Acceleration
Acceleration is DIRECTLY related to the size and direction of the force.
An object accelerates in the direction you push or pull it.

5. So….if you push twice as hard, it accelerates twice as much.
In other words….
Large Force = Large Acceleration a F
Small Force = Small Acceleration a F
So….if you push twice as hard, it accelerates twice as much.

6. But there is a twist….
Acceleration is INVERSELY related to the mass of the object.

7. In other words…..using the same amount of force….
Small acceleration a
Large Mass
Large acceleration F a
Small Mass

8. Newton’s Second Law
Newton, genius that he was, observed these “rules” of acceleration and came up with his second law of motion.
Newton’s 2nd law can be expressed in words or mathematically (as a formula).

9. Newton’s Second Law
The acceleration of an object depends on the mass of the object and the amount of force applied.
F = m x a
Force = Mass x Acceleration

10. Newton’s Second Law Key Point #1: More force  greater acceleration
More mass  less acceleration (for the same amount of force)

11. 2nd Law Summarized (Video)
1:14

12. Golf Ball vs Ping Pong Ball - DEMO

13. Golf Ball vs Ping Pong Ball - DEMO
They fall at the same time because… Gravity accelerates the two objects at equal rates

14. Golf Ball vs Ping Pong Ball - DEMO
(Veritasium video – Misconceptions about falling objects)
Veritasium video (3:22)
Point out that FORCE due to gravity is the WEIGHT of the object (that’s different)
Acceleration of each object is the same due to differences in inertia (that’s the same – why they

15. Sample Problem – Calculate the acceleration of an apple and watermelon when dropped off of a building.
Mass = 1.02 Kg
Force = 10 N
Mass = .102 kg
Force = 1 N

16. Hmm… does this mean they would land at the same time if dropped off of a building?
m/s2?

17. Hmm… does this mean they would land at the same time if dropped off of a building?
Why don’t we actually observe all objects falling at the same rate in Earth’s atmosphere?

18. Hmm… does this mean they would land at the same time if dropped off of a building?
Why don’t we actually observe all objects falling at the same rate in Earth’s atmosphere?
Air resistance slows down acceleration.
Air resistance is a type of fluid friction.
The amount of air resistance depends on the size and shape of the object.
Example: Feather vs Apple

19. Example Problems (p. 3)

20. Newton’s 2nd Law – Review
Explain why it is easier to throw a baseball than a bowling ball.
Why can 4 people push a broken down car off the road faster than just one person?
Why do the elephant and mouse land on the ground at the same time (theoretically) if they jumped out of a plane?

21. Newton’s 2nd Law Music Video
Newton’s 2nd Law Music Video