1. Newton’s Laws of Motion
Isaac Newton developed his 3 Laws of Motion (by the time he was 23!) to describe motion in the natural world.
According to Newton, why did the chicken cross the road?
Chickens at rest tend to stay at rest and chickens in motion tend to cross the road

2. Newton’s 1st Law of Motion
Newton’s 1st Law of Motion is a restatement of Galileo’s concept of inertia:
“Every object continues in its state of rest, or a uniform speed in a straight line, unless acted on by a nonzero force.”

3. Newton’s 1st Law of Motion
Old tablecloth trick
The brief friction between the dishes and the fast-moving tablecloth starts the dishes moving but then the friction between the dishes and the table stops the dishes before they slide very far.

4. Newton’s 1st Law of Motion
Force Block Diagrams
Used to show the different forces acting on an object.
Helpful for finding the net force
What forces are acting on the green box if it is still?
Normal force
Weight (Gravity)

5. Newton’s 1st Law of Motion
Force Block Diagrams
What forces are acting on the green box if someone is pushing it? N
Normal force
Pushing Force
Friction F P
Weight (Gravity) W

6. Newton’s 1st Law of Motion
Example: What is the force on the dog?
When will the dog move?

7. What is Acceleration?
Non-accelerated Motion Occurs when an object is moving at a constant velocity Problem 1
1 m
5 m
The ball reaches the wall with a speed of
1 m/s and takes a time of 5 seconds

8. What is Acceleration? Non-accelerated Motion Animal Distance Time
Speed
Cheetah
75 m
3 s
25 m/s
Greyhound
160 m
10 s
Gazelle
1 km
100 km/h
Turtle
30 s
1 cm/sec
Speed = Distance / Time

9. What is Acceleration?
What about Accelerated Motion? Acceleration occurs when the object is not moving at a constant speed
Time
Acceleration
Velocity
v = at
Distance
d = ½ at2
0 s
2 m/s2
0 m/s
0 m
1 s
2 s
3 s
4 s
5 s

10. Newton’s 2nd Law of Motion
Newton was the first scientist to recognize the connection between force and mass in producing acceleration.
Newton’s 2nd Law of Motion states:
“The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object.”

11. Newton’s 2nd Law of Motion
A simpler way to state Newton’s 2nd Law is: acceleration = net force mass

12. Newton’s 2nd Law of Motion
Question: Before we defined acceleration as the change in speed over time and now we are saying that acceleration is the ratio of force to mass – which is it? a = v/t or a = f/m
Acceleration is defined as that change in velocity over time but is caused by force applied to the mass

13. CHECK YOUR NEIGHBOR
Suppose in a high-flying airplane the captain announces over the cabin public address system that the plane is flying at a constant 900 km/h, and the thrust of the engines is a constant 80,000 newtons.
What is the acceleration of the airplane?

14. Newton’s 2nd Law of Motion
Sample Problem Suppose you apply the same force (1 N) to two different carts, one with a mass of 1 kg and the other with a mass of 2 kg. Which cart will accelerate more?
2 Kg
1 Kg
1 N
1 N
a= ? a = ?

15. How are you feeling about this concept?
Reflection
How well do you understand Newton’s 1st Law? How about his 2nd Law?
What can you do to improve your understanding?