1. GRAVITY AND NEWTON’S LAWS OF MOTION
CHAPTER 2 NOTES
GRAVITY AND NEWTON’S LAWS OF MOTION

2. GRAVITY AND ACCELERATION
ALL OBJECTS FALL TO THE GROUND AT THE SAME RATE.
THE ACCELERATION DUE TO GRAVITY IS THE SAME FOR ALL OBJECTS.
ACCELERATION DEPENDS ON BOTH FORCE AND MASS.

3. Why do all objects fall to the ground at the same time?
A heavier object has a greater gravitational force than a lighter object.
A heavier object is harder to accelerate because it has more mass (more inertia).
The extra mass balances the extra (increased) gravitational force so they fall at the same acceleration.
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4. ACCELERATION Rate at which velocity changes
Change in velocity divided by the amount of time that change occurs
All objects accelerate toward the Earth at 9.8 m/s/s
Every second that an object falls, the object’s downward velocity increases by 9.8 m/s

5. Calculating Velocity of Falling Objects
Change in velocity = gravity x time Gravity = 9.8 m/s/s A penny is dropped from the top of a tall stairwell. What is the penny’s velocity after it has fallen for 2 seconds? Change in velocity = 9.8 m/s/s x 2s = 19.6 m/s downward

6. The same penny hits the ground in 4. 5 seconds
The same penny hits the ground in 4.5 seconds. What is the penny’s velocity as it hits the ground?
Change in velocity = 9.8 m/s/s x 4.5 s
= 44.1 m/s downward
A marble at rest is dropped from a tall building. The marble hits the ground with a velocity of 98 m/s. How long was the marble in the air?
98 m/s = 9.8 m/s/s x T
= 98 m/s divided by 9.8 m/s/s = 10 seconds

7. An acorn at rest falls from an oak tree
An acorn at rest falls from an oak tree. The acorn hits the ground with a velocity of 14.7 m/s. How long did it take the acorn to land?
14.7 m/s = 9.8 m/s/s x T =
14.7 divided by 9.8 =
1.5 seconds

8. MORE PROBLEMS
A boy standing on a high cliff dives into the ocean below and strikes the water after 3 seconds. What is the boy’s velocity when he hits the water?

9. Velocity = 9.8 x 3
= 29.4 m/s downward

10. A foul ball is hit straight up in the air and falls from the top of its motion for 1.4 seconds before being caught by the catcher. What is the velocity of the ball as it hits the catcher’s glove?

11. Velocity = 9.8 x 1.4 =
13.72 m/s downward

12. A brick falls from the top of a building and strikes the ground with a velocity of 19.6 m/s downward. How long does the brick fall?

13. 19.6 m/s = 9.8 m/s/s x T
= 19.6/9.8 =
2 seconds

14. AIR RESISTANCE Force that opposes motion
Amount of air resistance depends on size, shape and speed of the object
More surface area slows the falling object down

15. TERMINAL VELOCITY When a falling object falls at constant velocity.
As speed of a falling object increases, air resistance increases. The upward force continues to increase until it is equal to the downward force of gravity. At this point the net force is 0 N and the object stops accelerating.

16. PHYSICS OF BUNGEE JUMPING!

17. FREE FALL
Object are in free fall only if gravity is pulling down and no other forces are acting on it.
Free fall can only occur if there is no air / air resistance (air resistance is a force). This would be in a vacuum or in space.

18. ORBITING
Astronauts float in orbiting spacecrafts because of free fall.
An object is orbiting when its traveling around another object in space.
A space craft travels forward, but at the same time gravity pulls it towards the Earth. This is orbiting.

19. CENTRIPETAL FORCE
Gravity provides the centripetal force that keeps objects in orbit.
Centripetal force is the unbalanced force that causes objects to move in a circular path.
This force keeps planets orbiting the Sun and moons orbiting their planets.

20. PROJECTILE MOTION
Projectile motion is the curved path an object follows when it is thrown or propelled near the surface of the Earth.
2 COMPONENTS combine to form a curved path:
1. Horizontal motion: The force given to an object such as throwing or kicking. This horizontal force is at constant velocity.
2. Vertical motion: the downward motion due to gravity. This velocity increases because of gravity.
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21. NEWTON’S 1st LAW
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.
Friction is an unbalanced force that will change an object’s motion.
Inertia – tendency for an object to resist motion

22. Newton’s 2nd Law
The acceleration of an object depends on the mass of the object and the amount of force applied.
Force = mass x acceleration
F=ma

23. FORCE = MASS x ACCELERATION
Which needs more force to accelerate at the same rate?
FORCE = MASS x ACCELERATION

25. Newton’s 3rd Law
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
All forces act in pairs. If a force is exerted, another force occurs that is equal in size and opposite in direction.
They do not always act on the same object.

26. MOMENTUM Depends on an objects mass and acceleration. P = m x v
Law of conservation of momentum: when objects collide, momentum is never lost; some can be transferred into the second object

27. SPORTS SCIENCE NFL – http://www.youtube.com/watch?v=F1FHm_EmcRw
Intro to 3 Laws
Newton’s 1st Law:

28. SPORTS SCIENCE Newton’s 2nd Law
Newton’s 3rd Law
Football vs soccer