Newton's First Law states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Friction is a net force that causes objects to slow down and stop due to contact between surfaces. According to Newton's First Law, without friction or gravity, objects would continue moving indefinitely. The net force on an object is calculated by adding all individual forces acting on it; if the forces balance out the net force is zero and there is no change in motion, while an unbalanced net force will cause acceleration or a change in speed or direction of motion.

1. Newton’s Laws of Motion

2. I. Newton’s First Law A. Also called, the law of inertia . B. Every object continues in a state of rest, or at a constant speed in a straight line unless acted on by an unbalanced , or a net force

4. 2. Why do things stop??? Friction – the force that resists the motion, or attempted motion, between objects in contact. Friction is the net force that changes an object’s motion.

5. Friction!

6. Without friction (OR gravity!) all things would continue to move in a straight line at a constant velocity!

7. C. Net force (unbalanced forces!) When more than one force acts on an object, the net force is the sum of all the forces. 5N 10N 15N

8. C. Net force (unbalanced forces!!) When opposing forces cancel each other out, the net force is zero 5N 5N Net Force = 0

9. If the forces do not cancel out, then you do have a net force! C. Net force (unbalanced forces!!) 10N 5N Net Force = 5N

10. Balanced vs. Unbalanced Forces!

11. Balance & Net Force??? Unbalanced Net Force Balanced F net = 0

12. Balanced Forces & Motion

13. Unbalanced Forces & Motion Change in velocity ↕ Acceleration ↕ Net Force! ↕ Unbalanced Force

14. Speeding up!

15. Slowing down!!!

16. Constant Velocity