1. Forces and the Laws of Motion

2. Forces • Force is a push or pull on an object. • Unit for force: N or Newton.

3. Balanced forces Where there are two forces that counteract each other and result in no movement (EQUAL) • Unbalanced forces One force is greater than the other force. (UNEQUAL)

4. Friction • A force that resists motion and can cause heat • Lubricants help reduce friction • Types of friction • Sliding • Rolling • Fluid • Static

5. Types of friction • Static • acts on objects that are not moving • Always acts in opposite direction to applied force • Sliding • Opposes direction of motion as an object slides • Less then static friction • Rolling • Friction that acts on rolling objects • 100 to 1000 times less than static and sliding friction • Fluid • Opposes the motion of an object through a fluid • Fluids include gases and liquids • Air resistance – fluid friction acting on an object moving • through the air

6. Newton’s Laws of Motion • 1st Law: Objects at rest remain at rest, or objects in motion remain in motion unless acted upon by a force. (unbalanced) • 2nd Law: The acceleration of a body depends on the ratio of the acting force to the mass of the body. (unbalanced) • F = m x a • 3rd Law: for every action there is an equal and opposite reaction. (balanced)

7. 1st Law of Motion (Law of Inertia) • Inertia: force that is resistant to the direction of the motion • The forces are Unbalanced • Examples: Inertia belts (seat belts)

8. 2nd Law of Motion • Concept: Acceleration • The forces are unbalanced • Examples: hitting a golf ball gently vs. hard. • F = ma Answer = _50__ newtons

9. Problem 1 How much force is needed to accelerate a 500.0 kg car at a rate of 4 000 m/s/s?

10. Problem 2 A 100 N force causes an object to accelerate at 2 m/s/s. What is the mass of the object?

11. Problem 3 A 1.5 kg ball is kicked with a force of 450 N. What acceleration did the ball receive?

12. 3rd Law of MotionAction/ Reaction • Concept: Action/Reaction of objects • Forces are balanced • Examples: Stationary objects, rockets being launched

13. Laws of motion Interactives http://science.discovery.com/games-and-interactives/newtons-laws-of-motion-interactive.htm

14. Projectile Motion Motion of a falling object after being given an initial forward velocity Combination of initial vertical force and downward force of gravity Causes object to follow a curved path

15. Gravity and Free Falling Objects • Gravity: The attraction between two objects. • All objects fall at a rate of 9.8 m/s2 • Gravity acts betweentwo masses • All masses exert the force of gravity – universal force • Galileo did an experiment at the leaning tower of Pisa in Italy with bowling balls. Both balls fell at the same rate.

16. Air Resistance • Force that slows down falling objects due to the atmosphere and surface area of the object.

17. Newton’s Law of Universal Gravitation • Shows that objects are attracted to one another in proportion to their masses and their distances away from the object.

18. Feather vs. Rock • Earth: feather would float down (air resistance) while the rock would drop at 9.8 m/s/s • Moon: feather and rock would drop at same rate due to no atmosphere and air resistance.

19. What about a vacuum? • vac·u·um[ vákyooəm ] • space empty of matter: a space completely empty of matter but not achievable in practice on Earth • space with all gas removed: a space from which all air or gas has been extracted • emptiness caused by absence: an emptiness caused by somebody or something's absence or removal • Both fall at the same rate due to there being no air.

20. Gravity and Weight Gravi ty Mass – measure of amount of inertia Weight – force of gravity pulling on an object Weight is product of mass and acceleration due to gravity ( 9.8 m/s/s) W = mg W- weight in newtons m- mass in kilograms g- acceleration due to gravity in meters per second squared