Transcript Kepler*s Laws and Gravity

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 –
•GRAVITY
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.
•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.
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.
• 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!
• https://www.youtube.com/watch?v=lbHt5mg_3
3w
• https://www.youtube.com/watch?v=sabH4bJsx
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