1. Physics 10/05/09 A magical Monday 1)Attendance – If your life had a theme song, what would it be? 2)Inertia 3)Reminder Lab Thursday

2. Newton’s Laws Newton’s First Law –An object at rest remains at rest and an object in motion stays in motion unless the object experiences a net force. Newton’s Second Law Newton’s Third Law

3. Inertia Object’s resistance to changes of motion –think of it as the “laziness” The greater the mass, the more inertia the object has. –Examples: »acceleration of a car and you are pulled back into the seat »driver hits the breaks hard and you fly forward »seat belt locking mechanism (below) When the brakes are hit, the red block slides forward due to inertia causing the ratchet to lock.

4. Acceleration is determined by net external force F gravity F ground F car F friction moving with constant velocity means all forces are balanced If the person takes his foot off the gas, the force from the car decrease and the net force is greater on the side of friction, thus slowing the car

5. F water F person F fish F gravity bobber only stays on surface if all force are balanced

6. A person is pulling a crate with a force of 70.0 N directed at an angle of 30 degrees above the horizon. There is a frictional force from the crate of 50.0 N. Is the crate moving? FyFy 30° F gr 50.0 N 70.0 N F g FxFx Since F net y = 0, we do not have to do any work there. Since this does not equal zero, the book would accelerate to the right.

7. Melissa leaves her Physics book on a drafting table that is inclined at an angle of 35 degrees. There is a gravitational force of 22N, a force from the table to the book of 18N, and a frictional force of 11N. Does the book move? We could use our trig function twice or we could rotate the x-y axes 35° to get the following: 18 N 11 N 35° 22 N 11 N 35 ° 22 N 18 N FyFy FxFx But we knew that because it had to equal the force from the table Yes, accelerates down the slope

8. A gust of wind blows an apple from a tree. As the apple falls, it has a gravitational force of 9.25 N and the wind exerts a force of 1.05 N to the right. Find the magnitude and direction of the net external force. 1.05 N 9.25 N 1.05 N F net θ 9.25 N