1. Forces Chapter 6.1

2. What You Already Learned Velocity is the ratio of the change in position of an object over a period of time. Acceleration describes a change in velocity of an object.

3. Acceleration What may cause an object to experience a change in velocity? – A is a or. –A may cause an object to speed up. –A may cause an object to slow down. –A may also cause an object to change direction.

4. Types of Forces

5. Force Force is a quantity, therefore it has both and. The SI unit for force is the. –The is a derived unit where: 1N = –1 is the amount of force required to accelerate a mass. –1 is about the weight of a medium sized apple.

6. Contact vs. Long Range Some forces act over distances while others act only when two objects are in contact with one another. – exist when two objects are in contact with one another. –Long-range () forces act over distances without a need for. forces and are long-range forces.

7. The System and Environment The object of interest is called the. The area around the object is called the. FgFg FNFN

8. Diagram FgFg FNFN = F N = Force of Desk on Book F g = Force of Gravity on Book diagrams provide a means by which all the acting on a system can be summarized and accounted for, and the determined. System

9. Newton’s Law Newton determined that the of an object is to the applied to move it and to the of the object. Where F = Force in Newtons m = of the object a = of the object

10. Newton’s 2 nd Law and Force vs. Acceleration How does acceleration relate to force? –As the force on an object, the rate of acceleration will. –i.e. Bigger = Bigger Acceleration m1m1 m2m2 ___ > ___ Note: The slope of the line in a F vs. a graph will equal the of the object. The greater the slope, the greater the

11. Newton’s 2 nd Law and velocity vs. time (constant force) Newton’s 2 nd Law indicates that a constant force applied to an object will cause the speed to change at a. i.e. is Time Note: Remember from kinematics that the slope of the line is equal to.

12. Newton’s 2 nd Law / Different Mass If the applied force to a system is held constant and the mass is increased from m 1 to m 2, what would a velocity vs. time graph look like? Time m1m1 m2m2 = Acceleration. ___ > ___ Force is Constant

13. Newton’s 2 nd Law / Different Force If the mass is held constant and the force applied to a system is increased from F 1 to F 2, what would a velocity vs. time graph look like? Time F2F2 F1F1 = Acceleration. ___ > ___ Mass is Constant

14. Example: What is the rate of acceleration? Two people are pushing a stalled car. The mass of the car is 1850 kg. One person applies a 275 N force while the other applies a 395 N force. A third force of 560 N acts in in the opposite direction compared to the two people. What is the acceleration of the car?

15. Diagram the problem F net =

16. State the Known and Unknowns What is known? –Mass (m) = kg –Force of person #1 (N) = N –Force of person#2 (N) = N –Opposing Force (N) = N What is not known? –Acceleration (a) = ?

17. Perform Calculations F net = Where: oF net = Substitute for F net and solve for a: o = + - oa = o If there was no opposing force, how would the rate of acceleration change? o What do you think is the source of the opposing force?..

18. Key Ideas Force is a quantity that is a measure of the magnitude of a push or pull in Newtons. Forces exist as or. Use to represent forces when problem solving. Newton’s 2 nd Law of Motion states that the rate of acceleration of an object is to the applied and to its mass. –A constant force applied to an object will cause it to accelerate at a. –As force, increases. –As mass, decreases.