1. Do Now
Susan’s displacement is 12 m left. First she walked 20 m left. How far right did she walk?
Dan’s resultant velocity in a boat is 8 m/s right. The wind is blowing him 2 m/s left. How fast is the boat motor moving him?

2. Objectives
Types of Forces
Free-body Diagrams
Net Force

3. Contact Field Types of Forces Normal Magnetic Friction Electric
Applied
Spring
Air resistance
Tension
Field
Magnetic
Electric
Gravitational

4. Applied Force (Fa) - An applied force is a push or pull acting on an object by another object or person.
Normal Force (FN) - the support force exerted upon an object which is in contact with another stable object.
Directed perpendicularly to the support surface.

5. Frictional Force (Ff) - force exerted by a surface as an object moves across it or makes an effort to move across it.
opposite direction of motion
Rough surface  more friction
The result of molecules from each object creating instantaneous bonds with each other.

6. Mass vs Weight
Mass (m)
the amount of matter in an object.
SI unit is kilograms (kg)
Is the same at every location.
Gravitational Force (Fg) - the force with which the earth, moon, or other massive body attracts an object towards itself. This is the weight of an object.
Varies depending upon location, mass, acceleration due to gravity.
Fg = mg

7. A 500 kg car has a weight of about 5000N on Earth
A 500 kg car has a weight of about 5000N on Earth. On the moon gravity is about 1/6 that on Earth. What would the mass and weight of the car be on the moon?

8. Free-body Diagrams
-represents object as a point particle with all forces acting on it drawn as vectors.

9. Example 1: Object moving at a constant velocity
Example 1: Object moving at a constant velocity. X forces balance and y forces balance Note: Typically the normal force and weight are equal if the object is on a flat surface moving left or right.

10. Example 2: Object accelerating
Example 2: Object accelerating. One force is greater than the other (unbalanced)

11. Net Force – the resultant force acting on an object
To find the net force acting on an object:
Add all y vectors (This = zero many times)
Add all x vectors
Add total x vector and total y vector to get the resultant force also called the net force.

12. Fnet=17N right
Net Force
FN=30N
Ff=9N
Fa=26N
Fg=30N

13. Find force D and E

14. Example Problem
A 6N box is pushed with a force of 17 N left. The net force acting on the box is 8N left. What is the force of friction acting on the box? Draw a free-body diagram.

15. Exit Pass
A 10N box is pushed to the left. The net force acting on the box is 15N left. Friction is 4N right. What is the applied force acting on the box? Draw a free-body diagram.