Newton’s Laws

1. Newton’s Laws Isaac Newton (1642 – 1727) The Father of Force

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

3. What is Force? F = ma Force= mass x acceleration Newton (N) (kg) (m/s2 ) newton Easier than saying kilogram m/sec2 N Is even easier!

4. 2 Kg Mass To Understand Force… You must understand the difference between Mass Weight AND

5. What is Mass? The amount of “matter” in an object 1 Kg Mass 1.5 Kg Mass 2 Kg Mass Mass is measured in kilograms.

6. How is Mass Different Than Weight? Weight is measurement of FORCE. 9.8 N 19.7 N 14.8 N (1 kg x 9.86 m/s2) F=ma (2 kg x 9.86 m/s2) (1.5 kg x 9.8 6m/s2) Acceleration due to gravity (9.8 m/s2) Acceleration due to gravity(9.8 m/s2) Acceleration due to gravity (9.8 m/s2) 1.0 Kg Mass 1.5 Kg Mass 2.0 Kg Mass DO NOT USEkilograms (kg) as a measurement for weight (force of gravity acting on a mass).

7. 100 Kg Mass is 220 lbs 7 Being pulled by different gravity? Your weight may be different. However, your mass never changes. On the moon220 lbs.would weigh 35 lbs. On the sun220 lbs.would weigh 5956 lbs. On Mars220 lbs.would weigh 82.9 lbs. What’s “Your Weight On Other Worlds?” http://www.exploratorium.edu/ronh/weight/

8. Newton's Three Laws of Motion These laws explain why objects move (or don't move). Let’s look at Newton's three laws of motion...

9. Newton's 3 Laws An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. 1 This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration 2 For every action force there is an equal and opposite reaction force. 3

10. Newton’s First Law: Balanced Forces An object will maintain a constant state of motion. (Speed and direction remain unchanged) This means an object at rest tends to stay at rest and an object in motion continues in the same direction with the same speed. Balanced Forces This is known as Inertia Stay in motion: a bowling ball tossed in space Stay at rest: a book on a table It will go on and on forever. Table pushes up on book IP&C Gravity pulls down on book

11. Newton’s First Law: Unbalanced Forces An unbalanced force is a force that changes the 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… The book below slides and then stops because of a resistant force called friction. Friction is force that opposes motion. It kind of reminds me of a few movies I’ve seen lately... Force of friction stops the book IP&C

12. 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!

13. Newton’s Second Law: Force = Mass X Acceleration Force and acceleration are related. 120 kg Lineman 100 kg Center F = ma F =ma Scenario # 1 Look at the situation above. If the acceleration 3 m/s2 from the snap was equal between these players, then who would have the advantage of force? Lineman = 3 m/s2 x 120 kg is 360 N Center = 3 m/s2 x 100 kg is 300 N The lineman has the advantage. Scenario # 2Now, let’s say the center has a 1 m/s2 advantage over his opponent at acceleration of 4 m/s2 from the snap. Now who has the advantage of force? Lineman = 3 m/s2 x 120 kg is 360 N Center = 4 m/s2 x 100 kg is 400 N Now, the center has the advantage.

14. Solving Force Problems Step 1 Read the problem. Draw a picture. Step 2 Write down what you know, What are you trying to find? Step 3 Set up the formula. Step 4 Plug-in the numbers. Solve.

15. Consider the problem… “How much force is needed to accelerate a 1400-kg car 2 m/s2? ” Step 1 Read the problem. Draw a picture. 1400-kgcar How much force? 2 m/s2 Formula Plug-in Answer F = m = a = Units, units, units!

16. “How much force is needed to accelerate a 1400-kg car 2 m/s2? ” Step 2 Write down what you know, What are you trying to find? 1400-kgcar 2 m/s2 Formula Plug-in Answer ? F = 1400 kg m = 2 m/s2 a = Units, units, units!

17. “How much force is needed to accelerate a 1400-kg car 2 m/s2? ” Step 3 Set up the formula. Solve. F = m x a Formula Plug-in Answer ? F = 1400 kg m = m x a 2 m/s2 a = Units, units, units!

18. “How much force is needed to accelerate a 1400-kg car 2 m/s2? ” Step 4 Plug-in the numbers. Solve. 2800 kg x m/s2 Formula Plug-in Answer ? F = 1400 kg m = F = ma 2800 kg x m/s2 1400 kg x 2 m/s2 2 m/s2 a = Units, units, units!

19. Be sure to do the problems. • Helpful Hints: a = F / m F = m x a m = F / a

20. The unit for force: newton 1 kg x m/s2 = 1 newton or 1N Which one would you rather write for your answer? 2800 N …I thought so.

21. Newton’s Third Law: Action Forces = Reaction Forces 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.

22. Newton's 3 Laws An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will continue with constant speed and direction, unless acted on by an unbalanced force. 1 This law shows how force, mass and acceleration are related as shown in the equation below: Force = mass x acceleration 2 For every action there is an equal and opposite reaction. 3

23. Forces and Geological Processes… Most of the time the Earth’s massive plates push on each and move very slowly. But, sometimes a massive plate exerts a greater amount of force that accelerates another plate. Results in an earthquake. To learn more about earthquakes: http://vcourseware5.calstatela.edu/VirtualEarthquake/VQuakeIntro.html Gravitational Force and waterfalls Results in erosion

24. The Story of Newton’s Apple Newton sat under an apple tree, and an apple fell on his head. That falling apple gave him a revelation and led him to describe a force called GRAVITY. But DON’T think of gravity as falling… It is the pull(force) that an object has on another object.

25. Gravity is the force that ALL objects in the UNIVERSE exert between each other... Newton said that gravitational force depends on 2 things: The DISTANCE of the objects The MASS of the objects More Fg Less gravitational force compared to... Less Fg The blue objects have more gravitational force between them than the Green objects. This is because the Blue objects have more MASS. more gravitational force here.

26. The acceleration due to gravity is known as “g.” When calculating FORCE due to gravity… F=ma should be rewritten as Fg = m x g

27. The apple and the Earth exert the same gravitational force. Fg = Fg Why is the apple pulled toward the Earth rather than the Earth pulled toward the apple? Why doesn’t the Earth move towards the apple?

28. Acceleration of AppleIs greater thanAcceleration of the Earth The apple moves faster toward the Earth than the Earth moves toward the apple. Gravitational force (Fg) being equally exerted… ma = ma Theapplehasvery little (m) mass compared to the Earth (m).

29. The moon is a satellite too.. The pull of gravity keeps satellites orbiting around the Earth.

30. 29 Satellites are sent away and placed in the exact spot where the Earth’s gravity pulls them into a “continuous free fall” or orbit... The moon does the same thing. The Earth is round and the satellite continues to “just miss” entering into the Earth’s atmosphere.

31. Does the moon’s gravitational pull affect the Earth? Yes, the moon’s gravity is large enough to actually pull water out of the ocean from space… Well, not quite that much...just enough to create motion of the tides.

32. Newton is even credited with inventing CALCULUS. Needless to say, Newton was very important in shaping our understanding of science.