Force and Laws of Motion

1. Unit 3 Lesson 7 Force and Laws of Motion S.8.C.3.1.1,2 The physics classroom website

2. Force 1 N= 0.225lbs • A push or pull on an object. • Can change the motion of an object • Measured in Newtons (N) (kg*m/s2) • Friction and gravity are examples. • Friction • A force that acts against motion. • Between objects that are touching • Between the legs of a desk and the floor when you push a desk

3. Gravity • A force that pulls matter together • Between objects that are not touching • Isaac Newton • “the force of gravity acts between all objects in the universe” • Gravity exists between all matter • Gravity exists between you and your pencil however it is very weak • The more mass an object has, the stronger its gravity • Keeps objects in orbit around a star, planet or moon. • Makes objects “fall”

4. Combining Forces Force Diagrams: • We use arrows to show the different forces acting on objects • Direction of arrow shows the direction the force is acting • Length of the arrow shows the strength (size or magnitude) of the force • Net force: the combination of all forces acting on an object 5N = = 10N 5N 5N 10N = 5N 5N 5N = 0 N

5. Balanced Forces • When two forces are the same strength (magnitude or size) but acting in opposite directions on a the same object. • Cannotchange an objects motion (speed and direction) • An object at rest to start with balanced forces will continueat rest • An object moving at 30 mph to the left with balanced forces acting on it will continue to move at 30 mph to the left • Forces are equal • Motion remains the same • If not moving, it continues to not move • If moving , it continues to move exactly the same

6. Balanced Forces Forces on the person are balanced: Gravity pulls down on person, chair pushes up on person 10 N 10 N

7. Unbalanced Forces • Will change an objects motion (speed and direction) • A net force results. • Net force is calculated by adding forces in the same direction or subtracting forces in opposite directions • If an object is starting at restwhen a net force of 40 N  is applied, the object will move to the right • If an object is already moving to the right at a constant speed when a net forceof 40 N  is applied, the object will speed up. • Net force of 40 N to the Right • 40 N • New motion depends on the starting motion

8. Newton’s 1st Law of Motion Law of Inertia • Object at rest will remain at rest • Object in motion will continue in motion in a straight line • The tendency of an object to resist a change in motion. • The higher the mass of an object , the higher its inertia is. Unless an unbalanced force acts upon it Circular motion animation car making a sharp turn

9. Inertia Video Clip Bill Nye- Inertia

10. Newton’s 2nd Law of Motion • F = MA • The larger the net force on an object , the more the objects motion will change (greater acceleration). • Objects with larger masses, need more force to change their motion.

11. Newton’s 2nd Law of Motion

12. Newton’s 3rd Law of Motion • When one object exerts a force on another object, the second object exerts an equal but opposite force on the first object • They are not balanced forces because the forces act on different objects 100 N 100 N

13. Newton’s 3rd Law • Action-Reaction • For every action (force), there is an equal but opposite reaction (force) 3 laws Video clip Newton’s 3 Laws