1. Objective
SWBAT use Newton’s first and second laws to identify and explain changes in the velocity of objects.

2. The man who follows the crowd will usually get no further than the crowd. The man who walks alone is likely to find himself in places no one has ever been. —Albert Einstein.

3. Balanced Forces  No acceleration

4. Newton’s First Law

5. Check For Understanding
Which statement below correctly summarizes Newton’s first law?
When a force acts on an object, the object accelerates in the direction of the force.
When the net force acting on an object is zero, the object stays at rest, or if the object is already moving, it continues to move in a straight line with a constant speed.
When unbalanced forces act on an object, the object will not move.
When balanced forces act on an object, the object will accelerate.

6. Supertankers illustrate the principal of inertia; their engines are cut off a mile or more before the tanker enters port and it still coasts right on in.

7. You are driving in a car with no seat belt on
You are driving in a car with no seat belt on. You see a family of ducks and slam on your brakes to avoid hitting them. Since you are not wearing your seat belt, you fly out of the car (remain in motion) until you hit the ground (an unbalanced force).
AHH!
Ouch
In motion…
At rest…

9. Unbalanced Forces  Acceleration

10. Forces are either balanced, or unbalanced
When forces are equal, no acceleration occurs.

11. Forces are either balanced, or unbalanced
But when they are unbalanced, that’s when objects accelerate

12. Forces are either balanced, or unbalanced
But when they are unbalanced, that’s when objects accelerate

13. Forces are either balanced, or unbalanced
But when they are unbalanced, that’s when objects accelerate

14. Forces are either balanced, or unbalanced
But when they are unbalanced, that’s when objects accelerate

15. Newton’s Second Law

16. Check For Understanding
If an object is accelerating, which statement below is true?
The object is being acted on by balanced forces.
The object is being acted on by unbalanced forces.
The object is not being acted on by any forces.
You do not know whether the forces are balanced or unbalanced.

18. If F = ma…
The more force you put in, the more acceleration an object will have.
If I throw the ball really hard
(F = 10 N), then the ball will
go really fast, (A = 20 m/s2)
If I throw the ball softly
(F = 1 N), then the ball will
go slowly, (A = 2 m/s2)

19. Newton’s Second Law
The more mass an object has, the more force you have to put in to move it.
It would be hard to move an elephant (more force), because he is so heavy (more mass).
It would be easy to move a baby duck (less force), because he is so light (less mass).

20. Newton’s Second Law
If you exert an equal force on two objects, the lighter object (the one with less mass) will accelerate faster.
F = 10 N

21. Check For Understanding
What property of a stalled car determines how much effort is required to move it?
Height
Mass
Volume
Length

22. Check For Understanding
Elrick pushes a textbook and a file cabinet. The textbook has a mass of 10 kg. The file cabinet has a mass of 300 kg. He pushes them both with a force of 50 N. Which box will accelerate at a faster rate?
The textbook
The file cabinet
They will accelerate at the same speed
Neither will accelerate – they will move with constant velocity.

23. Check For Understanding
Tanesha is mad at Maegan and Jahina, but she is REALLY mad at Maegan. She pushes Maegan with a force of 40 N, and she pushes Jahina with a force of just 5 N. If Jahina and Maegan have the same mass, who will accelerate faster after being pushed?
Jahina
Maegan
They will accelerate at the same speed
Neither will accelerate – they will move with constant velocity.