1. FORCES AND THE LAWS OF MOTION

2. What is a force? A force is a push or a pull and can cause an object to move, stop, or change direction. When 2 forces act together in the same direction, they are added. Opposite direction, you subtract. Unbalanced force = movement Balanced force = no movement

3. Forces

4. What Opposes Motion? Friction – will cause a moving object to slow down and/or stop. Acts in opposite direction. A. Sliding friction – solid slides over solid B. Rolling friction – wheels or ball bearings are added; lessens friction. C. Fluid friction – where fluids slow down falling objects.

5. More on Friction

6. Newton’s Laws 1665 – 1666 Isaac Newton developed 3 laws of motion. Inertia – the tendency of objects to remain in motion or stay at rest. Related to mass: bigger object = harder to move or stop.

7. Law # 1 1 st law – an object at rest will remain at rest; an object in motion will remain in motion; unless acted upon by a force. Ex: you’re in a car moving 45 mph and you have to slam on the brakes; the car stops but you keep moving forward.

8. Law # 2 2 nd law – Force (1 N) = Mass (kg) x Acceleration Force is measured in newtons. Ex: How much force is needed to accelerate a 1400 kg car 2m/sec/sec? 1400 x 2 = 2800 N

9. Newton’s 1 st and 2 nd laws…

10. Law #3 3 rd law – For every action, there is an equal and opposite reaction. Ex: walking (you push down and back but you move up and forward); a rocket.

11. Newton’s 3 rd law…

12. Just cuz it’s funny…

13. Which law does this represent? And…why?

14. Let’s take a poll? (don’t write any of this) If you could drop an elephant (assume he wouldn’t be hurt) and a golf ball off the Eiffel Tower; which would hit the ground first? Let’s test your theory… (with a book and a pencil off the desk…which hits first?)

15. Gravity Acceleration of a falling object is due to the force of gravity is 9.8 m/sec/sec. 1 meter = 9.8 m/sec/sec 2 meters = 19.6 m/sec/sec 3 meters = 29.4 m/sec/sec Galileo proved this first using cannonballs of different sizes.

16. Gravity

17. Then why doesn’t everything fall at the same rate? Air resistance Did you know that terminal velocity is where sky divers “float” because the force of air holding them up equals the pull of gravity. Elephant and a feather!

18. Skydiving…

19. What did Newton conclude…? Newton’s Law of Universal Gravity – ALL objects have the force of gravity. Bigger it is…more gravity it exerts.

20. Weight and Gravity Weight – the measure of the pull of gravity on an object. You weigh less on a mountain top verses sea level. Why? Weight = mass x 9.8m/sec/sec Ex: What would the weight be of an object with a mass of 10kg? 10 x 9.8 = 98 N

21. Weight…

22. The Wright Brothers Do NOT write! December 17, 1903 Wilbur and Orville Wright stand on a deserted beach near Kitty Hawk, NC. Orville climbs in their creation and a 12 horsepower gas engine. They are about to try something that no one else has ever succeeded at before. They are going to fly their machine.

23. HISTORY IS MADE…

24. Fluid Pressure Pressure –is a push/force and is exerted equally in all directions. Pressure = Force/Area Hydraulic Devices – used to raise heavy objects. Ex: barbers’ chairs, brakes on cars, and rescue ladders.

25. Differences in Pressure Fluids move from high to low pressure. Ex: a vacuum cleaner works by creating a low pressure zone causing the high pressure area outside to rush in carrying all the particles with it.

26. How does this affect humans?

27. Pressure and Gravity Pressure and Gravity –the pressure of any fluid varies with depth. Higher altitude = lower pressure and lower depths = higher pressure

28. Shoulder Partner Why would this happen? When divers go too deep and then resurface too quickly their body rids of nitrogen bubbles too quickly causing “the bends”. This is quite painful and dangerous. Divers must surface slowly to prevent this.

29. The Bends

30. Buoyancy Buoyant force- upward force that acts against the downward weight of the object. Archimedes Principle - the buoyant force on an object is equal to the weight of the fluid displaced. Salt Lake

31. Floating… An object floats when it displaces a volume of fluid whose weight is greater than or equal to its own weight.

32. Archimedes Principle

33. More on floating… An object will also float if the density of that object is less than the density of the fluid. Density of water is 1g/cc Wood is.8 g/cc Aluminum is 2.7 g/cc Which floats the wood or the aluminum?

34. So…what really controls buoyancy?

35. Applying the Concepts…please explain the following scenarios. Why can this fly? Why did one sink and the other did not?

36. Flight Bernoulli’s principle – (in simple terms) says that moving air creates lower pressure than the area around it. Ex: smoke goes up a chimney because wind blows by the top, you have to run to fly a kite. An airplane wing is designed so that air passing over the wing travels faster than air passing beneath it. Causing high pressure under the wings to hold the plane up… DEMO

37. More on Bernoulli’s

38. Hovercraft race…