1. Is it always equal to the weight (mg) of the object? Why or why not?
Pre-Do Now:
What is a normal force?
Is it always equal to the weight (mg) of the object? Why or why not?
When you stand up, what part of you is in contact with the floor? Try standing on one foot, what do you notice and what does this have to do with the normal force?

2. Do Now:
Mr. Rao is really strong, so he pulls with a 120 Newton force 30o above the horizontal to the right. His 10kg dog resists with a horizontal 40 Newton Force in the opposite direction. DRAW A FBD!!!
What is the NET force acting on the dog?
B. What is the dog’s acceleration?

3. Aim: How do we define equilibrium in a system?
HW: Newton’s Law WS

4. Equilibrium Object is at Rest
Object is moving at constant speed in a straight line.

5. Demo 1 Block in air “Force” “Force” Spring scale Spring Scale
“Not Moving”
***Is the block at equilibrium?
YES!!! It’s not moving!
Two students do this

6. 4 Steps for Newton’s Law Problem
Draw a Free Body Diagram
Sum up vertical and horizontal forces SEPERATELY.
Write Newton’s Second Law for vertical and horizontal!
Solve for Unknown

7. Demo 2 Block in air Force 2 Force 1 Force 3
***Is the block at equilibrium?
YES!!! It’s not moving!
Let 3 students do this and solve for one left out force. After math is done, show physics works!
F1 = F2 + F3

8. Demo 3 Block on Table Draw Free Body Diagram and label forces
Block is in contact with something, so must be a force!
Block is in contact with something, so must be a force.
Weight = force of earth on block. (wont get right away)
Fn = Force of table on block

9. Summary
Solve for the forces described using the 4 Step Method!

10. A Block resting on a table is pushed down on with a force of 10 N, but is also being pulled on to the right by two people with a force of 12 N and pulled on to the left by one person. The block is not moving and has a mass of 10 kg. What forces will make the statement true?