Target Thursday January 3, What is gravity? 2.How do you know it is there? 3.What causes gravity? 4.Name 3 things that are in motion in this room right now

Gravity: a force of attraction between objects that is due to their mass

-All matter has mass -All matter experiences gravity

The earth’s mass is large, therefore its gravitational pull is large

British scientist Sir Isaac Newton developed the “Law of Universal Gravitation”

Gravity

What is Gravity? Gravity=FORCE! Gravity is a force of attraction. Gravity PULLS.

Matter & Gravity Facts All matter has mass. All matter experiences gravity. All objects experience a gravitational attraction toward each other.

Law of universal gravitation All objects in the universe attract each other through gravitational force. The size of the force depends on mass and distance.

Gravity depends on…… Mass & Distance

Law of Universal Gravitation Part 1: Gravitational force increases as mass increases

Gravity and Mass Greater mass=greater gravitational pull. Earth’s gravitational force is due to it’s enormous mass.

Law of Universal Gravitation Part 2: Gravitational force decreases as distance increases

Gravity and Distance Closer together=greater gravitational pull.

Which ones have more gravitational pull? Vs.

Which ones have more gravitational pull? Vs.

Now which ones? Vs.

Mass Amount of matter in an object. Does not change with location. Unit=grams Weight Measure of the gravitational force exerted on an object. Changes with location. Unit=Newtons A newton is the amount of force it takes to accelerate 1 km of mass 1 m/s

Force - a push or pull The combination of all forces acting on an object is the net force.

Balanced Force Two or more forces exerted on an object are balanced if their effects cancel each other and do not cause a change in the object’s motion. The net force is zero.

Unbalanced Force Occurs when the forces acting on the object changes the object’s motion. The net force is NOT zero.

Target What determines the gravitational force of an individual object? 2.What would cause the force of gravity to be greater between two objects if their mass stays constant? 3.Why would you weigh less on the moon? 4.What two different instruments measure mass and weight?

BRAINPOP rcesandtime/gravity/ rcesandtime/gravity/

Friction - is a force that resists the sliding between two touching surfaces. Friction is an opposing force Friction will always slow a moving object.

Types of Friction Static friction causes surfaces to stick together. It keeps an object at rest. Sliding friction slows down an object that slides. Rolling friction is needed to make a wheel turn. Fluid friction is air and/or water resistance.

INERTIA The tendency of an object to remain at a constant speed unless another force acts upon it. If it is moving at a certain speed it will stay at that speed unless a force acts on it. If it is still, then it will stay still unless a force acts on it

NEWTON’s LAWS of MOTION

Newton’s 1 st law sometimes called “Law of Inertia” Inertia: the tendency of all objects to resist any change in motion

Newton’s 2 nd Law: The acceleration of an object depends on the mass and the amount of force Force = mass x acceleration

Newton’s 3 rd Law: When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

Objects in motion have momentum because they have mass. Momentum is conserved.

Gravity and Motion

Acceleration due to gravity Rate at which velocity changes because of the pull of gravity. Earth= 9.8 m/s/s

Acceleration due to gravity (g)

Gravity & Acceleration due to gravity All objects fall at the same rate because the acceleration due to gravity is the same for all objects. All objects accelerate toward Earth at 9.8 m/s/s Air resistance, a type of friction slows down acceleration.

Air resistance is the force of friction and the opposing force created by going through the air.

Terminal velocity When an object falls at a constant velocity because the air resistance force matches the force of gravity. Net force=0

Would a parachute work on the moon? No air resistance, so no.

Target What is acceleration due to gravity? 2.What causes terminal velocity? 3.What is terminal velocity? 4.What is inertia? 5.What is momentum?

Brainpop rcesandtime/newtonslawsofmotion/ rcesandtime/newtonslawsofmotion/

Free Fall Free fall- when gravity is the only force acting on an object (free fall acceleration is directed toward center of earth) The acceleration of gravity (g) for objects in free fall at the earth's surface is 9.8 m/s 2. Galileo found that all things fall at the same rate in the absence of air resistance, regardless of their mass

Orbiting objects are in free fall.

So if all objects experience gravity, then can something ever be weightless? No. When an object is “weightless” it is really falling and hasn’t hit an object yet.

Free Fall The rate of falling increases by 9.8 m/s every second. Height = ½ gt 2 For example: ½ (9.8 )1 2 = 4.9 m ½(9.8)2 2 = 19.6 m ½ (9.8)3 2 = 44.1 m ½ (9.8)4 2 = 78.4 m

Air Resistance In air… –A stone falls faster than a feather Air resistance affects stone less In a vacuum –A stone and a feather will fall at the same speed.

Free Fall A ball thrown horizontally will fall at the same rate as a ball dropped directly.

Free Fall A ball thrown into the air will slow down, stop, and then begin to fall with the acceleration due to gravity. When it passes the thrower, it will be traveling at the same rate at which it was thrown.

Projectile motion-curved path an object takes when thrown near the surface of the Earth.

2 parts of projectile motion: Horizontal Motion Force of throw. Across Vertical Motion Gravity pulling downward. Down

How does projectile motion occur?

1) Which object will hit the ground first: an apple or a feather?

Earth: The apple will not experience air resistance like the feather, so the apple will fall first. Moon: They will both hit the ground at the same time because there is no air resistance.

2) Why is the Earth round?

All the mass is pulled in because of gravity.

3) This drawing shows an enlarged person holding a rock. If he threw the rock slightly to his right, what path would the rock take? Show what happens to the rock by drawing a line showing the complete path of the rock, from the person's hand to where it finally stops.

Projectile Motion:

4) With enough force, would it be possible for the rock never to hit the Earth?

Could be thrown into orbit around the Earth.

5) What weighs more: a pound of feathers or a pound of bricks?

They each weigh the same. The Earth’s gravity pulls on the objects the same.

6) Is gravity a pull or a push?

Pull.

7) True or False Weightlessness is not because one is in space: it’s because one is falling! Space has gravity just like everywhere else, just no fixed objects to hold against to keep from falling

True

8) True or False Everything that has mass has a gravitational pull.

True

9) True or False Astronauts on the Moon were not weightless! The Moon has gravity much like the Earth. But since the Moon is less massive, the gravitational pull is smaller. The astronauts were pulled to the Moon with about 1/6th the force of gravity back here on Earth.

True

Galileo and Pisa U5tjNCY U5tjNCY JZI&feature=related JZI&feature=related

Projectile Motion An object thrown upward at an angle to the ground follows a curved path called a parabola. combines vertical and horizontal motion Orbiting objects- forward motion combines with free fall and object follows a curved path

Free Fall Review Dropping something from a resting position (gains speed as it falls so it accelerates) Gravity pulls objects down (air resistance can affect how fast) (no air resistance- in a vacuum) When gravity is the only thing that affects falling object → FREE FALL Acceleration due to gravity is 9.8 m/s 2

-TAKE A QUIZ FROM THE BACK DESK -YOU HAVE 10 MINUTES TO COMPLETE THIS QUIZ

Illustrated Dictionary For each term, write the word, the definition, and give an illustration with color Put your name in the box with Momentum -Newton’s First Law -Newton’s Second Law -Newton’s Third Law -momentum -projectile motion -free fall -terminal velocity -air resistance

Target Do Newton’s Laws work in space? 2.Why do astronaut’s have to exercise while in space? 3.Why do astronauts get taller while in space?

Target Read “Determining Net Force” on pages Read “Balanced and Unbalanced forces” on pages Answer questions 2-5 on page 127

Force Problems There is a box sitting on the floor. Gravity is pulling down on the box with 9.8 N of force. The ground is applying the normal force to the box at 9.8N. One man is pushing the box to the left with 25N of force and his friend is playing a joke on him by pushing the box with 20N of force to the right. What is the Net force on the box? Is this balanced or unbalanced force? Diagram the forces on the box.

Force Problems A plane is flying through the air. Gravity is pulling down on the plane with a force of 9.8N. The Lift created by the plane’s wings is pulling up on the plane with a force of 9.8N. The force of friction is pulling back on the plane with a force of 10N. The thrust of the engines is propelling the plane forward with a force of 10N. What is the net force on the plane? Is this balanced or unbalanced? Diagram the forces on the plane.

Target Write one paragraph consisting of 6-8 sentences describing one of Newton’s Laws. Be sure and give at least one descriptive example.

Writing Topic Writing Situation The Earth, the moon, and Jupiter all have different masses; therefore they have different gravitational pulls. Directions for Writing Write an essay comparing and contrasting your life on Earth with the Moon and Jupiter. Remember that the Moon has 1/6th the gravity of Earth and Jupiter has 2.5 times the Earth's gravity. In your answer include specific examples about reduced and increased gravity. What are some of the adjustments you would need to make?

Friday January 18, 2013 Take a Quiz from the basket on the back desk You have 10 minutes to complete the quiz