CHAPTER 2 NOTESGRAVITY AND NEWTON’S LAWS OF MOTION

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.

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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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

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

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

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

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?

Velocity = 9.8 x 3

= 29.4 m/s downward

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?

Velocity = 9.8 x 1.4 =

13.72 m/s downward

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?

19.6 m/s = 9.8 m/s/s x T

= 19.6/9.8 =

2 seconds

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

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.

PHYSICS OF BUNGEE JUMPING!

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.

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.

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.

PROJECTILE MOTIONProjectile 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.

http://www.youtube.com/watch?v=ymgMNLPw1yY&list=PLuqizYjiBk2R9juOqfbN78K9h_K5b7OrW

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

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

Which needs more force to accelerate at the same rate?

FORCE = MASS x ACCELERATION

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.

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

SPORTS SCIENCE

NFL –

http://www.youtube.com/watch?v=F1FHm_EmcRw

Intro to 3 Laws

http://www.youtube.com/watch?v=MAm6LOUnJ80

Newton’s 1st Law:

http://www.youtube.com/watch?v=F9COtJBBzhk

SPORTS SCIENCE

Newton’s 2nd Law

http://www.youtube.com/watch?v=nJTKiS444BQ

Newton’s 3rd Law

http://www.youtube.com/watch?v=9k48c9Z1VjY

http://www.youtube.com/watch?v=hTZI-kpppuw

Football vs soccer

http://www.youtube.com/watch?v=LQy8dFco_xY