1. Physics Physics Tutoring Tuesday: 2:15pm – 3:15pm

2. 5-Minute Warm-Up OBJECTIVE: Use force summation and Newton’s First Law to determine unknown forces acting on an object. Two men attempt to move a box up a ramp. One pulls the box with a rope, and the other pushes the box from behind. While they are working, a dog jumps on top of the box and lays down. Draw a Free-Body Diagram of the box.

3. Summing and Solving For Forces If a = 0, then ΣF = 0 (Σ stands for “sum of”)

4. Example #1 A 2kg can rests on a table with a 5kg book on top of it. What is the normal force on the can?

5. Summing and Solving For Forces (1) (1)Draw A Free Body Diagram (2) Draw an x and y axis on your FBD (3) Assign Positive and Negative Direction (4) Sum the forces in each direction using a force chart. Vertical forces are independent of horizontal forces. (5) If the object is not changing motion, then ΣF =0. Write equations to solve for unknowns.

6. Example #2 Tug of war! On one side, a 70 and 30 N force. On the other side, a 45N force and another person. How hard does the fourth person have to pull to stay even? To win?

7. Example #3 A 5kg road sign is supported by two metal poles. What is the supporting force from each of the two poles?

8. Example #4 A bird sits on top of a birdhouse that has a mass of 3.5kg. If the normal force on the birdhouse is 37N, what is the mass of the bird?

9. Example #5 A warehouse worker pushes a refrigerator across the floor with a force of 200N. If the friction force is only 10% of the normal force, what is the magnitude of friction? What will happen to the motion of the box?