Do NowMonday, 4/2

Take our your notebook and answer the following question:

What is the difference between weight and mass?

You have 4 minutes. I will come around to check your answer!

12.2 Gravity

Key Ideas:1. How are weight and mass related?2. Why do objects fall to the ground when dropped?3. What is the relationship between free-fall acceleration and

mass?4. Why does a projectile follow a curved path?

Key Terms

1. Weight2. Free Fall3. Terminal Velocity4. Projectile Motion5. Component6. Mass

1. A measure of the gravitational force exerted on an object.

2. The motion of a body when only the force of gravity is acting on the body.

3. The constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity.

4. The curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth.

5. A part of something.6. The amount of matter in an object.

Demo

What force is keeping this balloon in my hand?

Once I flick the balloon off my hand does gravity still affect the balloon when it is in motion?

Weight and Mass

What is weight? On Earth, your weight is simply the amount of

gravitational force exerted on you by Earth.

Near Earth’s surface, the free-fall acceleration, g, is about 9.8 m/s2.

On the moon, g is only 1.6 m/s2.

Weight and Mass

You can use F=ma (Newton’s 2nd Law) to calculate a body’s weight.

Thus, weight is equal to mass times free-fall acceleration.

weight = mass x free-fall acceleration

w = m x g

Weight is measured in Newtons (N)

Weight and Mass

Would an object be the same mass on Earth as they would be on Mars or the Moon?

Would an object be the same weight on Earth as they would be on Mars or the Moon

What is the difference between weight and mass?

Weight and Mass

Weight influences shape Gravitational force affects the shapes of living

things.

A ball has a mass of 6 kg. Calculate the weight in Newtons.

m =

g =

w =

If an object has a mass of 25 kg on earth, determine both the mass and the weight of that same object on the moon.

m =

g =

w =

If a bag of fruit weighs 5 Newtons, calculate its mass in kilograms.

m =

g =

w =

Physical Science4/9/15

Grab your notes off of the front lab table and answer the following question.

Explain why dropping something off of a building and pushing something off of a building are different.

You have 5 minutes

Law of Universal Gravitation

No matter how small or large the object, it exerts this force on every other object.

The force of gravity between two objects involves:

1) 2 masses

2) distance between the 2 masses

Law of Universal Gravitation

Gravitational force is weak between objects that have small masses.

Gravitational force is stronger when one or both objects are larger.

Gravitational force rapidly becomes weaker as objects move farther away from each other.

Law of Universal Gravitation

When Earth’s gravity is the only force acting on an object, the object is said to be in free fall.

Free-fall acceleration is directed toward the center of Earth.

Law of Universal Gravitation

Universal Gravitation = everything that has mass has gravity

Both air resistance and gravity act on objects moving through Earth’s atmosphere. When a sky diver reaches terminal

velocity, the force of gravity is balanced by air resistance.

Law of Universal Gravitation

Astronauts in orbit are in free fall

Are objects weightless in space?

No because they are still in

close to other massive objects which have weak gravitational forces. So nothing can be truly weightless.

In the orbiting space shuttle, which is in free fall, astronauts experience apparent weightlessness.

Projectile Motion

What is projectile motion?

What are some other examples of projectile motion?

Projectile motion has two components:

1) Horizontal

2) Vertical

Projectile Motion

Horizontal component: Horizontal motion is motion that is

perpendicular, or at 90˚ angle, to the Earth’s gravitational force.

After you have thrown a ball, no horizontal forces are acting on the ball (if air resistance is ignored).

So the horizontal component of velocity of the ball is constant after the ball leaves your hand. Ignoring air resistance, when it is small, allows one to simplify projectile motion.

Projectile Motion

Vertical component If not affected by gravitational acceleration, the

ball would continue moving in a straight line and never fall.

When you throw a ball, gravity pulls it downward, which gives the ball vertical motion.

Projectile Motion

1) After the ball leaves the pitcher’s hand, its horizontal velocity is constant.

2) The ball’s vertical velocity increases because gravity causes the ball to accelerate downward.

3) The two motions combine to form a curved path.

Projectile Motion

You can see the different components of motion here.

The yellow ball was given a horizontal push off the ledge. It follows a projectile-motion path.

The red ball was dropped without a horizontal push.

Inquiry Questions

1. Explain why your weight would be less on the moon than on Earth even though your mass would not change.

2. State the law of universal gravitation, and use examples to explain how changes in mass and changes in distance affect gravitational force.

3. Explain why free-fall acceleration near Earth’s surface is constant.

4. Name the two components that make up orbital motion, and explain why objects stay in orbit.

5. Explain why the gravitational acceleration of any object near earth is the same no matter what the mass of the object is.