1. Chapter 4
Newton’s Laws

2. Sir Isaac Newton Came up with three laws of motion
Also wrote the Law of Universal Gravitation

3. Newton’s First Law of Motion
1st Law: An object at rest will stay at rest and an object in motion will stay in motion UNLESS acted upon by an outside force.
Only an unbalanced force can cause motion to change
Remember, a force is a push or pull

4. First Law Cont.
If a car traveling at 65 km/hr suddenly stops, why would you fly forward?
Why is it important to wear a seatbelt?
An astronaut out in space throws a ball. What would happen to the ball?
What are the unbalanced forces that stop the motion of the matchbox car?

5. First Law Cont. The first law is also known as the law of inertia.
Inertia: the tendency of an object to resist change in motion.
The more mass an object has, the more inertia it has.
Science of Football

6. First Law Cont.
Which will change its velocity more easily: a 12 pound bowling ball traveling at 2m/s or a ping pong ball traveling at 2m/s?
Which has more inertia:

7. Newton’s Second Law
2nd Law: the acceleration of an object is in the same direction as the net force on the object and that acceleration equals the net force divided by the mass.

8. Second Law Cont. Objects with more mass take more force to accelerate.
The smaller the mass, the greater the rate of acceleration.
The greater the unbalanced force acting on an object, the greater the acceleration.

9. Second Law Cont. The second law can be shown in these formulas:
Force = Mass * Acceleration or F = M * A
M = F / A
A = F / M

10. Second Law Practice
Units: Force is Newtons, Mass is kilograms, and Acceleration is m/s2
How much force is needed to move a 900kg object 32 m/s2?

11. Second Law Practice Cont.
What is a car’s mass if the net force is 3000N and has an acceleration of 2 m/s2?
If the mass of a helicopter is 4500kg and the net force is 18000N, what is its acceleration?

12. Newton’s Third Law
3rd Law: when one object exerts a force on a second object, the second object exerts a force on the first object equal in strength but opposite in direction.
Put simply, for every action, there is an equal and opposite reaction.

13. Third Law Examples
Your foot pushes on the floor with 50N. The floor pushes back in the opposite direction with 50N.

14. Newton’s Law Explained
Newton’s Cradle

15. Momentum
Momentum: property of a moving object that equals its mass times velocity
Think: how much force is needed to change an object’s motion?
Which has more momentum: a 10lb bowling ball moving at 2 m/s or a 1lb softball moving at 1 m/s?

16. Momentum Cont. Momentum = Mass * Velocity
This equation is shown as P = M * V
Units: Mass is kg, Velocity is m/s and Momentum is kg*m/s

17. Momentum Practice
A car with a mass of 1300kg travels at a speed of 28m/s. What is the momentum?
A baseball travels at 40m/s and has a mass of .15kg. Momentum?

18. Law of Conservation of Momentum
The Law of Conservation of Momentum states that when objects exert forces only on each other, the total amount of momentum stays the same.

19. Law of Conservation of Momentum Examples

20. Law of Conservation of Momentum Examples

21. Law of Conservation of Momentum Examples

22. Law of Conservation of Momentum Examples

23. Gravity 4-2

24. What is Gravity? Gravity is the attractive force between two objects.
All objects made of matter have gravitational attraction.
The force of gravity is affected by two factors:
The mass of objects
The distance between the objects

25. Mass and Distance
The more mass an object has, the greater the gravitational pull.
Ex: Gas giants have more moons around them than the smaller, inner planets.
The closer one object is to another, the stronger the gravitational pull.
Ex: Sun and moon both have a gravitational pull on Earth, but Earth’s is stronger since we are closer to it.

26. Newton’s Law of Universal Gravitation
Law of Universal Gravitation: a mathematical calculation between mass and the distance between two objects.
F = G m1m2 D2
Force = gravitational acceleration * mass of the first object * the mass of the second object divided by the distance squared.

27. L.U.G. Cont.
This equation simply states the strength of gravity depends on the masses of objects and the distances between them.
The gravitational acceleration of objects close to Earth’s surface is 9.8 m/s2

28. Gravitational Acceleration
If a bowling ball and a tennis ball are dropped from the same height in a vacuum (no air resistance), then both hit the ground at the same time.
WHY???
All objects in the absence of air resistance accelerate at 9.8 m/s2 close to Earth’s surface

29. What two factors keep planets and moons in orbit?
GRAVITY and INERTIA

30. Weight VS Mass
Weight: a measurement of the gravitational pull on an object
Mass: the amount of matter in an object

31. Weight VS Mass Cont.
Why are you weightless in outer space, yet still have the same mass?
On which planet would you weigh the most?
Free Fall and Weightlessness

32. Projectile Motion
Projectile: any object that is thrown or shot through the air
Why do projectiles fall in a curve?
Due to CENTRIPETAL ACCELERATION, an object will accelerate on a curved path. As velocity changes, the object will have a curved path.

33. Centripetal Force
Centripetal Force: the net force applied to an object traveling in a circular path.
DEMO: the bucket and the dime
Video just in case

34. When you throw a ball out of a canoe, the ball moves forward but the canoe moves backward.
1st Law
2nd Law
3rd Law

35. When you are standing in a subway train, the train suddenly stops but you go forward.
1st Law
2nd Law
3rd Law

36. A little girl was pulling a sled in the snow
A little girl was pulling a sled in the snow. She stopped to tie her shoe, but the sled kept moving and hit her in the back of the leg.
1st Law
2nd Law
3rd Law

37. It is easier to carry your backpack when it is empty.
1st Law
2nd Law
3rd Law

38. Two bumper cars collide and bounce back.
1st Law
2nd Law
3rd Law

39. A boy is going down a slide
A boy is going down a slide. As he reaches the bottom, friction causes him to slow down and stop.
1st Law
2nd Law
3rd Law

40. When you give your friend a lift on your bike, you have to pedal harder and faster to keep the same speed.
1st Law
2nd Law
3rd Law

41. A smaller cannon ball leaves a cannon much faster than a larger, heavier cannon ball fired from the same cannon.
1st Law
2nd Law
3rd Law