1.What is the unit for force? 2. What is the force weight of a 45 kg desk? 3. Give a scenario example for each of Newton’s Laws.

4. What is net force? Give an example.

CatalystNewton

(N)

441 N

HANDS UP!!

Total of ALL forces acting on an object

Gravity is a force of attraction between objects caused by their massesAll matter has mass.

Gravity

Gravity is a result of mass.

So, all matter is affected by gravity.

ALL objects have a gravitational attraction to each other – YES, ALL OBJECTS! We don’t notice this attraction because it is so small that it appears insignificant.

Gravity

Why must you exert a force to pick up an object? What must you overcome?

You must overcome GRAVITY to lift any object.

WHY??

Isaac Newton…

The Falling Apple story…Newton sat under a tree and saw an apple fall and thought there had to be forces at work – he called the force gravity.

Fig, I mean Isaac Newton!

7 Steps that led Newton to being considered the “MAN”Step1—Understand Galileo’s concept of Inertia.

Any change in speed or direction requires a force.

Step 2—Sit under apple tree.

Step 3—See apple falling on head; see moon through trees.

Step 4—Realize that the moon must be falling

towards the earth, just like the apple!

Step 5— Wonder why moon circles Earth.

Step 6— Conclude that a centripetal force must be pulling the moon into circular motion.

Step 7—Figure out that the moon falls for the same reason that the apple falls—both are pulled by

EARTH’S GRAVITY.

Part 1: Gravitational force Increases as MASS Increases.

Part 2: Gravitational force Decreases as DISTANCE Increases.

It is valid EVERYWHERE in the UNIVERSE!

Larger mass = Larger Gravitational force; Smaller mass = Smaller Gravitational force

Universal Law of Gravitation

Diagram it!

The moon will remain in motion in a straight line if it were not acted upon by an outside force (the Earth’s gravity pulling on it).

How Universal Gravitation relates to Newton’s First Law…

Weight is a measurement of how hard gravity is pulling on that object.

Your weight depends on how much gravity is acting on you at the moment and varies by your location

Mass: amount of matter in an object; does NOT change based on location

Weight vs. Mass

Weight Mass

Changes based on location

Always stays the same

Measured in Newtons

Measured in Grams

Tool: Spring scale or digital scales

Tool: balance or digital scale

1N 100g

Table it!

How do they compare? 180 lbs on

Earth

81 kg on Earth

0 lbs in space

81 kg in space

Which weighs the most on Earth?

Which weighs the most in space?

Which one??

This is NOT a new formula…

Gravitational Force = Weight

So if

then

where g = 9.8m/s2 and m = mass in grams

Weight = mg

Background: have you ever jumped up and down on a scale, what happens to your weight?

Objective: See how changing acceleration can add or take weight away

Materials: (1) spring scale/group

(2) Weight, anything you can find

Spring Scale Practice (10 min.)

How does the mass of an object relate to the gravitational force that the object exerts on other objects?

The gravitational force on Jupiter is approximately 2.3 times the gravitational force on Earth. If an object has a mass of 70 kg and a weight of 686 N on Earth, what would the object’s mass and weight on Jupiter be?

Review 1

The larger the mass, the larger the force and vice versa.

Mass = 70 kg (stays the same) ; Weight = 2.3 X 686 N = 1577.8 N

How do you explain to someone who has no knowledge of gravity that gravity exists in space?

Why does your weight change if you landed on Mars, but your mass does not?

Review 2

Weight is a measure of gravitational force, while mass is constant

Gravity holds the planets in orbit around the sun.

Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects.Check out these videos: http://www.youtube.com/watch?v=z_sJ15feNGw and http://www.youtube.com/watch?v=aRhkQTQxm4w

Gravity and Acceleration

How fast is it moving when it hits the ground?

Acceleration Due to Gravity…for every second that an object falls, the object’s downward velocity increases by 9.8 m/s.

Velocity of falling objects formula: ∆v =

g × t 

Let’s Practice!

Check out these videos to review Terminal Velocity:

http://www.youtube.com/watch?v=4qeCcvq2_io

http://www.youtube.com/watch?v=V_wnJ84AFmI

OK…your turn…SUMMARIZE it!

Terminal Velocity Check!!!

Centripetal acceleration is acceleration in a circular motion; it is CONSTANTLY accelerating – WHY??

It is CONSTANTLY changing direction!

Consider the example of swinging a cup of water in a circle.

What happens?

Video: http://www.youtube.com/watch?v=56QCI4Ig4EY

Centripetal Acceleration

The unbalanced force that causes objects to move in a circular path is called a centripetal force.

Gravity provides the centripetal force that keeps objects in orbit.

Orbiting and Centripetal Force

Free Fall Occurs When There Is No Air Resistance An object is in free fall only if gravity is pulling it down and no other forces are acting on it.

A vacuum is a place in which there is no matter. Objects falling in a vacuum are in free fall because there is no air resistance.

Free Fall on a ride: http://www.youtube.com/watch?v=JzKZNm1lcDc

Free Fall

Projectile motion is the curved path an object follows when it is thrown or propelled near the surface of the Earth.

Projectile motion has two components—horizontal motion and vertical motion. These components are independent, so they have no effect on each other.

Projectile Motion

Projectile Motion

Horizontal Motion is a motion that is parallel to the ground.

When you throw a ball, your hand exerts a force on the ball that makes the ball move forward. This force gives the ball its horizontal motion.

Horizontal Motion

Vertical Motion is motion that is perpendicular to the ground.

A ball in your hand is prevented from falling by your hand. After you throw the ball, gravity pulls it downward and gives the ball vertical motion.

Vertical Motion

He hypothesized that the moon was simply a projectile circling the Earth under the attraction of gravity.

YOUR TURN AGAIN…SUMMARIZE IT!!

Newton’s Hypothesis…

What is the acceleration due to gravity on Earth?

Why do all objects on Earth fall at the same acceleration?

What are the 2 parts of the Universal Law of Gravitation?

Compare Mass and Weight. UNITS too!

Formulas for calculating gravitational force and velocity of a falling object.

HOMEWORK!!! Answer in COMPLETE sentences! EXIT TICKET!!