1. September 23, 2011 What is inertia?
How does mass affect an objects ability to remain in motion?

2. Today
Notes
Newton’s 1st Law Demos

3. What is Newton’s First Law of Motion?
Examples:
When you come to an abrupt stop in a car, your body moves forward.
If you have a table set for dinner, you can pull the table cloth out from under the glasses and dishes without disturbing them.

4. What is Newton’s First Law of Motion?
When objects are resting or in motion, they will remain the same unless something else (a force) acts on the object

5. What is Newton’s First Law of Motion?
The object will continue with the same speed and direction, therefore have a constant velocity unless something makes it change.
Ex. If a ball is rolling down a hill, it will continue to roll until something stops it or causes it to change direction.

6. What is Newton’s First Law of Motion?
The idea that objects in motion stay in motion and objects that are at rest remain at rest is called INERTIA
Newton’s First Law of Motion is called the Law of Inertia
***Which direction would the ball
travel if released at this point?

7. If this is true, than why does a ball eventually stop rolling in the hallway?
Friction is an outside force, which causes the ball to stop rolling
In our world, it is hard to show Newton’s 1st law because we always have some outside forces

9. How is a seatbelt an “inertia preventer?”
A person in a car should continue to travel forward (an object in motion remains in motion) but the seatbelt prevents that

10. What’s a force?
Any influence that causes something to change speed or direction
“push or a pull”
Examples: gravity (pull), friction (pull)

11. What’s a force? Measured in Newtons (N)
Vector Quantity: includes a number and direction
What are the other vector quantities we’ve talked about?
Velocity (non vector relative is speed!)
Displacement (non vector relative is distance!)

12. What’s a force?
If you push on a wall with a force of 10 N and the wall pushes back with a force of 10 N, the wall will not move because the overall force is 0 N.
The overall force applied
on an object is called the
NET FORCE

13. What’s a force?
When the net force is 0 N, we say the object is in equilibrium (equilibrium sounds like EQUAL!)
The Equilibrium Rule states forces acting upward on an object must be equal to those acting downward.

14. What’s a force?
This is how scales work. Scales are a measure of the “support force” (also known as a normal force) pushing upward against your weight pushing downward.
Your weight is a downward
force which is measured by
the scale you stand on.

15. What’s a force?
The idea that there are opposing forces explains why we can’t “walk thru walls” or fall thru the floor.

16. Homework
Parts 6 & 7
Check out some of the Newton Demos!