BellringerGive the date and the name for the day in

which the southern hemisphere will be experiencing the most direct sunlight and

have the longest amount of daylight hours.

Gravity and MotionNotes

Gravity• The strength of the force of gravity between two

objects depends on two factors: the masses of the objects and the distance between them.

• A force is a push or pull.

• Gravity is the force that attracts ALL objects towards each other. Gravity does not need contact between objects. Gravity causes a book to fall if the book is dropped.

• Newton’s Law of Universal Gravitation states that every object in the universe is attracted to every other object in the universe.

• Apple is to head as the moon (Luna) is to Earth.

Gravity• Mass is the amount of matter in an object.

The more mass an object has, the greater the force of gravity.

• Book to you vs. Book to floor

• Weight is the effect of gravity on an object with mass. The less gravity, the less the object weighs.

• Because of gravity, Earth pulls on the moon. The moon also pulls on Earth. The moon stays in orbit around Earth because of gravity.

Gravity• The force of gravity is stronger when two objects are

close together. The force of gravity gets weaker if the two objects are farther apart.

• The force of gravity decreases exponentially as distance is increased.

• For example, if to objects of finite mass move a distance twice as far apart, then the gravitational attraction will decrease by a factor of 4.

• If the same objects move 3 times as far apart from their original position, then gravity decreases by a factor of 9.

• 4 times farther apart from their original position would see gravity decrease by a factor of ____?

Inertia and Orbital Motion

• Isaac Newton concluded that two factors - inertia and gravity - combine to keep Earth in orbit around Sol, and Luna in orbit around Earth.

• Newton’s first law of motion states that an object at motion will stay in motion in the same direction, at the same speed, unless acted upon by another force. An object at rest will remain at rest until acted upon by another force.

• This tendency of an object to not change its motion is called inertia.

Inertia and Orbital Motion

•Suppose that you are in a car that stops suddenly. You will keep moving forward because of inertia.

•If the car turns sharply, you body will have a tendency to continue in the same direction that you were moving before the turn, so your body appears to lean in the direction opposite of the turn.

Inertia and Orbital Motion

• If the sun and Earth are constantly pulling on one another, why doesn’t Earth crash into the sun?

• Similarly, why doesn’t the moon crash into Earth?

• There must me another force acting on these objects to keep them from flying into the objects that they are attracted to.

• Enter inertia.

Inertia and Orbital Motion

•The moon wants to fly away from Earth off in a straight line. Earth’s gravity is constantly pulling the moon towards it. This creates the illusion that the moon does nothing but circle Earth, or Earth circles the sun.

Newton’s Cannon

http://waowen.screaming.net/revision/force&motion/ncananim.htm

Einstein’s Gravity•Newton’s laws explained almost

everything about gravity except its most important question:

•Why are objects attracted to each other?

•Newton’s laws worked perfectly well, for the most part, but he had no explanation for the existence of the original attractions.

http://einstein.stanford.edu/Media/Newtons_Universe_Anima-Flash.html

Einstein’s Gravity• Einstein’s Theory of General Relativity

developed the idea that space was actually a four-dimensional property known as space-time.

• Using this idea, he stated that a massive object that rotates will warp space-time around it.

• To visualize this, think of a bowling ball sitting in the middle of a mattress.

• When another rotating object is nearby, the object will orbit along the curvature of the space-time warping.

• To visualize this, think of the coin vortex in the mall, where the coin will spin around and around the central hole.

Einstein’s Gravity

http://einstein.stanford.edu/Media/Einsteins_Universe_Anima-Flash.html