1. Forces Intro #4 (New Pink) May the Forces be with you.....

2. 1) Force: a push or pull on an object Has its own unit….. The Newton (N) Has its own unit….. The Newton (N) Anytime you see something moving… a force caused it. Anytime you see something moving… a force caused it. Where is this jeep exerting a force? What’s keeping it from moving? What’s keeping it from moving?

3. What are some forces you cannot see? What are some forces you cannot see? Write Down 3 Write Down 3 Wind Wind Water Water Underwater currents at the beach Underwater currents at the beach Magnets Magnets Gravity Gravity Static cling Static cling

4. 2) Forces in combination The net force is the result of 2 or more The net force is the result of 2 or more forces acting on a object. forces acting on a object. Forces combine in 2 ways....... Forces combine in 2 ways.......

5. Forces in the same direction are added together Julio was pulling at the front of the car (20N) and Alex was pushing at the back (35N). Julio was pulling at the front of the car (20N) and Alex was pushing at the back (35N). What was the net force? What was the net force? 20 N + 35 N = 55 N 20 N + 35 N = 55 N

6. Forces in Different Directions are subtracted. Subtract the smallest from the largest Subtract the smallest from the largest Vader and Snow were in a Vader and Snow were in a rough tug of war for the rope. Vader was pulling 55 N. Snow was pulling 57 N. Vader was pulling 55 N. Snow was pulling 57 N. What was the net force? What was the net force? 57 N – 55 N = 2 N 57 N – 55 N = 2 N

7. Practice Jorge, Tony, and Chris were all pushing a Chris were all pushing a couch into the other room. What is their net force? Jorge 13 N, Tony 14N, Chris 17 N 13N + 14N + 17N = 44N Sharon and Destiny were both pushing on opposite sides of a soda machine attempting to rock it. What is their net force? What is their net force? Sharon 13N, Destiny 14 N 14N – 13 N = 1 N 14N – 13 N = 1 N

8. Unbalanced vs. Balanced Forces Unbalanced Net force is not zero so there is a change in motion Net force is not zero so there is a change in motion Ex. Car was pushed and pulled, snow won the tug of war Ex. Car was pushed and pulled, snow won the tug of war Can also include a change in direction… Can also include a change in direction… Ex. Kicking a Soccer ball Ex. Kicking a Soccer ball Balanced Forces acting on an object that cancel each other out... = no motion! Ex. Hat resting on your head… what forces are generated? This also called Equilibrium

9. There are two forces acting upon the book. Since these two forces are equal size (also called magnitude) and opposite directions, they balance each other out. The forces are balanced so the book is not moving either direction. It is in equilibrium.

10. Again (because it’s important!) When the forces are balanced, the net force is zero. When the forces are balanced, the net force is zero. When the net force on an object is zero, we say the object is in equilibrium. When the net force on an object is zero, we say the object is in equilibrium.

11. Equilibrium and normal forces A normal force is created whenever an object is in contact with a surface. A normal force is created whenever an object is in contact with a surface. The normal force is equal to the downward force (weight.) The normal force is equal to the downward force (weight.)

12. Another example of a balanced force A person standing upon the ground is in equilibrium. (What is the normal force observed here?)

13. Solving equilibrium problems For an object to be in equilibrium, all the forces acting on the object must add to zero. For an object to be in equilibrium, all the forces acting on the object must add to zero. Do not mix forces in the horizontal direction with forces in the vertical (up and down) direction. Do not mix forces in the horizontal direction with forces in the vertical (up and down) direction. What is the net force on this block? Will it move?