Newton’s Laws of Motion

1. Newton’sLaws of Motion https://www.youtube.com/watch?v=aA_mqSzbkM0

2. Sir Isaac Newton • 1. Described 3 laws that relate forces to motion • 2. Force-a push or a pull, all forces have size and direction

3. Newton’s Laws of Motion 1st Law = An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. 2nd Law = Force equals mass times acceleration. 3rd Law = For every action there is an equal and opposite reaction.

4. Vocabulary • 1. Friction = a force that opposes motion between 2 objects that are touching • 2. Inertia = tendency of all objects to stay at rest or in motion • 3. Mass = the amount of matter an object is made of

5. Newton’s First Law An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force. https://www.youtube.com/watch?v=LEHR8YQNm_Q

6. What does this mean? Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force. If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving. It takes force to change the motion of an object.

7. Newtown’s 1st Law of Motion = “Law of Inertia” • An object at rest remains at rest and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force

8. 1st Law • Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. These pumpkins will not move unless acted on by an unbalanced force.

9. 1st Law • Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!

10. 1st Law • Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

11. What is this unbalanced force that acts on an object in motion? • There are four main types of friction: • Sliding friction: ice skating • Rolling friction: bowling • Fluid friction (air or liquid): air or water resistance • Static friction: initial friction when moving an object Friction!

12. Slide a book across a table and watch it slide to a rest position. The book comes to a rest because of the presence of a force - that force being the force of friction - which brings the book to a rest position.

13. In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.)

14. In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever.

15. Examples of Newton’s 1st Law of Motion • 1. Car suddenly stops and you strain against the seat belt • 2. Car turns left and you appear to slide to the right • 3. The difficulty of pushing a car that won’t start

16. Examples of Newton’s 1st Law of Motion

17. Newton’s 1st Law and You Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 km/hour. https://www.youtube.com/watch?v=wV2UTkkQ0Fg

18. Examples of Newton’s 1st Law of Motion A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion. Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion. https://www.youtube.com/watch?v=tMN36z8Zz4U https://www.youtube.com/watch?v=jpi6HjSYKcY

19. Newton’s Second Law Force equals mass times acceleration. F = ma https://www.youtube.com/watch?v=ZvPrn3aBQG8 Acceleration: a measurement of how quickly an object is changing speed.

20. 2nd Law F = m x a

21. What does F = ma mean? Force is directly proportional to mass and acceleration. Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force. Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball. Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.

22. Newton’s Second Law of Motion • The acceleration of an object depends on the mass of the object and the amount of the force applied

23. Newton’s Second Law of Motion • 1. Force = mass x acceleration F=m x a • 2. Force- a push or pull, all forces have size and direction • 3. Mass- the amount of matter an object is made of • 4. Acceleration-the rate at which velocity changes; and object accelerates if its speed changes, if its direction changes and if both speed and direction changes

24. Examples of Newton’s 2nd Law • 1. Hitting a softball, the harder the hit, the faster the ball goes • 2. Football players and their positions • 3. Loaded versus an unloaded truck

25. Examples of Newton’s 2nd Law

26. Examples of Newton’s 2nd Law

28. What does F = ma say? F = ma basically means that the force of an object comes from its mass and its acceleration. Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force. https://www.youtube.com/watch?v=EeT2yew0oDA

29. Newton’s Third Law For every action there is an equal and opposite reaction. https://www.youtube.com/watch?v=EgqcGrB3re8

30. 3rd Law According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

31. Think about it . . . What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).

32. Newton’s 3rd Law in Nature • Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water. • The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).

33. Newton’s 3rd Law in Nature Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

34. Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. • The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). • Action-reaction force pairs make it possible for birds to fly.

35. Other examples of Newton’s Third Law • The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction). https://www.youtube.com/watch?v=qLZC-2veBIs

36. Other examples of Newton’s Third Law The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases. The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction.

37. https://www.youtube.com/watch?v=yUp4W9htmuY Newton’s Laws of Motion 1st Law = An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. 2nd Law = Force equals mass times acceleration. 3rd Law = For every action there is an equal and opposite reaction.