Gravity F 34-40

Why would air make a difference? If you drop a ball and a feather from the same height at the same time, the ball would hit the ground first –This means the ball has fallen at a greater rate It is important to realize that when the ball and feather are falling they both pass through air air offers resistance to the motion of objects

Since the ball has more mass, the air resistance is greater on the feather than on the ball –This causes the ball to fall faster than the feather Scientists have learned that if you take away air resistance, objects of different weights will fall at the same rate (like on the moon)

What makes object fall at the same rate? Aristotle said that heavy things fell faster than lighter things –This was believed to be true until about 400 years ago In the early 1600’s Galileo challenged Aristotle when he said that things fall at the same rate –He was ignoring air resistance

To test his theory Galileo carried out experiments and concluded that : –object accelerate steadily as they fall –an objects weight (mass) does not affect how fast it accelerates when falling We know today that Galileo was right because we know about gravity –The attraction between the mass of Earth and the mass of an object

Objects with a large mass are pulled on by gravity with more force but they also have more inertia (resistance to change in motion) Because of this objects with greater mass will fall with the same acceleration as less massive objects

What is the acceleration of falling objects? There is a legend that Newton cam up with the idea of gravity from being hit on the head while sitting under an apple tree What is for sure is that Newton came up with the idea that there is an invisible force pulling objects to the ground This is the same force that keeps the Moon in the Earth’s orbit

In the case of a falling apple the unbalanced force acting upon the apple is gravity –We give the force of gravity on any object a name  weight It is the weight of the apple that makes it accelerate to the ground A combination of the Moon’s inertia and the force of gravity between the Earth and the Moon that keep it in orbit

How can gravity be universal? Newton said that as mass increases the force of gravity does also Newton’s Law of Universal Gravitation –The force of gravity between two objects increases with the mass of the object and it decreases with the distance between them squared It is universal because it applies to all objects not just moons, planets and stars Look at F 40 for times when added weight may be helpful