2. Force

3. What is a Force? Force can be defined as a push or a pull … or anything else that has the ability to change motion.

4. Units for Force kg x m/s 2 kilogram x m/sec 2 Newton is the scientific unit!!! N=kg x m/s 2

5. To Understand Force… You must understand the difference between AND 2 Kg Mass

6. What is Mass? 1 Kg Mass 2 Kg Mass 1.5 Kg Mass The amount of “stuff” in an object Mass is measured in k kk kilograms.

7. How is Mass Different Than Weight? Weight is a measurement of force!! Weight is a measurement of force!! Weight is not measured in kg, it is measured in pounds (lbs) or Newtons. Weight is not measured in kg, it is measured in pounds (lbs) or Newtons. Gravity has an effect on the weight, but not the mass!! Gravity has an effect on the weight, but not the mass!!

8. 1 Kg Mass 2.2 Pounds On the sun 1.0 kg would weigh 59.5 lbs. On Mars 1.0 kg would weigh 0.8 lbs. On the moon 1.0 kg would weigh 0.3 lbs. For example: Mass is the Same:1 kg But the WEIGHT… 7

9. Newton’s 3 laws of motion

10. Newton’s First Law: Balanced Forces An object will maintain a constant state of motion (balanced). This means an object at rest tends to stay at rest and an object in motion tends to stay in motion.

11. Forces that are balanced can be: Not in motion In Motion Stay in motion: body not restrained by a seat belt in car accident Stay at rest: a book on a table

12. IPC BOOK Table pushes up on book Gravity pulls down on book

13. Newton’s First Law: Unbalanced Forces The book slides and then stops because of a resistant force called friction. Friction is force that opposes motion. In space there is no resistance to cause friction, so a bowling ball would stay in motion...unless another object got in the way… An unbalanced force is a force that changes the motion.

14. Of course “frictional” force happens on earth... but, if you weren’t wearing a safety belt you would continue your motion… Do not let this happen to you; buckle up!

15. Inertia and Mass Inertia Inertia an object’s resistance to any change in motion an object’s resistance to any change in motion The amount of laziness The amount of laziness Objects with greater mass have ______ inertia Objects with greater mass have ______ inertia Greater Greater

16. Force and acceleration are related. Newton’s Second Law: Force = Mass X Acceleration An object will have greater acceleration if a greater force is applied to it Which will accelerate faster—a car with one person pushing it or the same car with eight people pushing it?

17. The mass of an object also affects acceleration. The mass of an object also affects acceleration. Smaller mass=faster acceleration Smaller mass=faster acceleration Which will accelerate faster—a car with two people pushing it or the same two people pushing a fully loaded gravel truck? Which will accelerate faster—a car with two people pushing it or the same two people pushing a fully loaded gravel truck? Newton’s Second Law: Force = Mass X Acceleration

18. How do we calculate force? Force involves mass and movement so therefore we calculate force by Force involves mass and movement so therefore we calculate force by Mass x acceleration Mass x acceleration V m F a

19. “How much force is needed to accelerate a 1400-kg car 2 m/s 2 ? ” Consider the problem… F = m = a = FormulaPlug-inAnswer Units, units, units! Step 1Read the problem. Draw a picture. 1400-kg car 2 m/s 2 How much force?

20. F = m = a = FormulaPlug-inAnswer Units, units, units! 1400 kg 2 m/s 2 Step 2Write down what you know, What are you trying to find? 1400-kg car 2 m/s 2 “How much force is needed to accelerate a 1400- kg car 2 m/s 2 ? ”

21. FormulaPlug-inAnswer Units, units, units! Step 3Set up the formula. Solve. F = m = a = 1400 kg 2 m/s 2 m x a “How much force is needed to accelerate a 1400-kg car 2 m/s 2 ? ” F = m x a

22. FormulaPlug-inAnswer Units, units, units! Step 4 Plug-in the numbers. Solve. 2800kg x m/s 2 F = m = a = 1400 kg 2 m/s 2 “How much force is needed to accelerate a 1400-kg car 2 m/s 2 ? ” m x a 1400 kg x 2 m/s 2 2800 kg x m/s 2

23. Quick Review Newton’s first law: Objects at rest stay at rest and objects in motion stay in motion with the same velocity unless acted on by a net force Newton’s first law: Objects at rest stay at rest and objects in motion stay in motion with the same velocity unless acted on by a net force Newton’s second law: F=ma Newton’s second law: F=ma So….objects will speed up, change direction or stop only if acted on by a net force So….objects will speed up, change direction or stop only if acted on by a net force

24. Questions: Why does my car slow down when I take my foot off the gas? Why does my car slow down when I take my foot off the gas? Why is hard for me to move a desk with a student sitting in it? Why is hard for me to move a desk with a student sitting in it? Friction

25. Friction Friction is a force that opposes motion between two surfaces that are touching Friction is a force that opposes motion between two surfaces that are touching It also changes the energy of motion into heat energy---try rubbing your hands together and feel the heat It also changes the energy of motion into heat energy---try rubbing your hands together and feel the heat

26. Types of Friction Static Friction Static Friction The friction between two surfaces that are in contact but not moving The friction between two surfaces that are in contact but not moving Sliding Friction Sliding Friction The friction that opposes the motion of two surfaces that are in contact and sliding past each other The friction that opposes the motion of two surfaces that are in contact and sliding past each other Rolling Friction Rolling Friction The friction between an object rolling and the surface it is rolling on The friction between an object rolling and the surface it is rolling on

27. Some things that affect motion! Air resistance Air resistance The opposition to something moving through the air The opposition to something moving through the air Depends on shape, size, and speed Depends on shape, size, and speed A good portion of the gas that cars burn is to overcome air resistance A good portion of the gas that cars burn is to overcome air resistance Terminal Velocity Terminal Velocity When an object’s weight matches the air resistance—it is the highest velocity that a falling object will reach When an object’s weight matches the air resistance—it is the highest velocity that a falling object will reach

28. Question What are the three variables that Newton’s Second Law of motion connects? What are the three variables that Newton’s Second Law of motion connects?

29. Newton’s Third Law: Action / Reaction For every action there is an equal and opposite reaction. Look at the picture below: What is the action? What is the reaction? As the gases push downward out of the rocket, The rocket is pushed upward by gases.

30. Gravity is the force that ALL objects in the UNIVERSE exert on each other... 2 things Newton said that gravitational force depends on 2 things: DISTANCE The DISTANCE of the objects MASS The MASS of the objects LESS gravitational force compared to... MORE gravitational force here. blue object green object blue object MASS The blue object has more gravitational force than the green object because the blue object has more MASS.