KEPLER’S LAWS AND GRAVITY ALSO KNOWN AS “EARTH’S GREATEST INVISIBIBLE FORCE” BY HEATHER MENDONSA

IT ALL STARTED WITH A QUESTION… Ancient astronomers thought that the Sun, Moon and planets moved in perfect circles. By building on each other’s observations and discoveries, we now understand about gravity and the role it plays in the universe. 1. Tycho Brahe was a Danish astronomer who measured the orbit of planets. 2. Johannes Kepler discovered that these objects instead follow elliptical paths. He wanted to know WHY they went in an elliptical path. 3. Isaac Newton found the answer. It was gravity. He developed three laws of motion and the law of universal gravitation.

KEPLER’S FIRST LAW – THE LAW OF ELLIPSES Planets are orbiting the sun in a path described as an ellipse. BUT WHY?

KEPLER’S SECOND LAW – THE LAW OF TIME An imaginary line joining a planet and the sun sweeps out an equal area of space in equal amounts of time. A planet’s speed is constantly changing as it orbits around the sun. A planet is fastest when it is close to the sun. It moves slower when it is further away from the sun. If we draw an imaginary line from the center of the planet to the center of the sun it would show that the planet moves in equal areas for each period of time.

KEPLER’S THIRD LAW – THE LAW OF HARMONIES Kepler's third law provides an accurate description of the period and distance for a planet's orbits about the sun. BUT – You don’t need to worry about this law. Save it for high school. *Extra credit opportunity – Describe the third law in a way your classmates can understand it*

PROBLEM – KEPLER’S QUESTION OF WHY STILL WASN’T ANSWERED. 70 years later, Isaac Newton had an answer. It was answered in one simple word – G R A V I T Y

SO WHAT EXACTLY IS GRAVITY? Gravity is the attraction between two masses. All objects that have mass also have a gravitational force. The larger the mass the more gravitational pull of an object.

NEWTON’S LAWS OF MOTION NEWTON'S LAWS OF MOTION There are three of them. They explain the motion of an object as resulting from the forces acting on the object. 1.

VOCABULARY Friction is the force between an object in motion and the surface on which it moves. Friction is the external force that acts on objects and causes them to slow down when no other external force acts upon them.Friction Inertia is the tendency of a body in motion to remain in motion. Inertia is dependent on mass, which is why it is harder to change the direction of a heavy body in motion than it is to change the direction of a lighter object in motion.Inertiamass Mass is the amount of matter in an object. /

LAW #1 – A BODY AT REST WILL REMAIN AT REST UNLESS ACTED UPON BY OUTSIDE FORCES The first law states that a body at rest will stay at rest until a net external force acts upon it and that a body in motion will remain in motion at a constant velocity until acted on by a net external force. This is also known as the law of inertia.forcemotionconstant velocity W H A T ????? Let’s break it down into pieces.

EXAMPLE 1 – ICE SKATING If you are ice skating, and you push yourself away from the side of the rink, according to Newton's first law you will continue all the way to the other side of the rink. We know this doesn’t really happen. Newton says that a body in motion will stay in motion until an outside force acts upon it -- This outside force is friction. The friction between your ice skates and the ice is what makes you slow down and eventually stop.

EXAMPLE 2 – SEAT BELTS If a car is traveling at 60 mph, the driver is also traveling at 60 mph. When the car suddenly stops, an external force is applied to the car that causes it to slow down. But there is no force acting on the driver, so the driver continues to travel at 60 mph. The seat belt is there to counteract this and act as that external force to slow the driver down along with the car, preventing them from being harmed.

EGG DROP DEMO MATERIALS NEEDED: Beaker with water and food coloring Raw egg Pie tin Toilet paper roll A Brave Student

PENNY ELBOW Materials needed: One penny for each student Some brave students

THINK YOU KNOW YOUR STUFF? WATCH THIS! 3w 3w WA WA

VOCABULARY Momentum (of a body in motion) the product of its mass and velocity. net force -The combination of all the forces that act on an object. Acceleration -The amount by which a speed or velocity increases (and so a scalar quantity or a vector quantity).

LAW #2 – FORCE AND ACCELERATION The second law states that the net force on an object is equal to the rate of change, or derivative, of its linear momentum.

Picture two balls of different mass, traveling in the same direction at the same velocity. If they both collide with a wall at the same time, the heavier ball will exert a larger force on the wall. This concept, illustrated in, explains Newton's second law, which emphasizes the importance of force and motion, over velocity alone. It states: the net force on an object is equal to the rate of change of its linear momentum. From calculus we know that the rate of change is the same as a derivative. When we the linear momentum of an object we get:

EXAMPLE 1 – FORCE – MASS X ACCELERATION

EXPERIMENT WITH MASS: BALLS AND DICE Materials needed for each group: 1)3 unifix cubes 2)1 die 3)2 rulers 4)3 balls with different masses 5)Worksheet for lab information 6)Students who like to have fun

YOU WILL WRITE YOUR OWN LAB NOTES FOR THIS EXPERIMENT. BE NEAT! KEEP YOUR DATA IN YOUR LAB NOTEBOOKS

NEWTON’S THIRD LAW: FOR EVERY REACTION, THERE IS AN EQUAL AND OPPOSITE REACTION