Newton's First Law of Motion: Inertia
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Video Lecture 2 of 46
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Date Added: February 5, 2015

### Lecture Description

The MASS of a body is a measure of its inertia. The WEIGHT of a body is the FORCE with which the Earth pulls on it. MASS is - as we say -invariant - it is the same everywhere; WEIGHT varies from place to place. NEWTON'S FIRST LAW has to do with INERTIA. It says this: A body at rest wishes to remain at rest; a body in uniform motion in a straight line wishes to do this. Allthe demonstrations in this program near on these great ideas.

A - We show a block of mass M. IT wants to remain at rest "so much" . A block of mass 2M wants to remain at rest TWICE AS MUCH. So too on April Fool's Day does a package of bricks behave!

B - The HEAVY block with the dowel-rod handle stays at rest if it is at rest; it keeps on going if THAT is what it is doing.

C - We show a sequence of simple, utterly-simple, plebeian DEMONSTRA¬TIONS bearing out the strength and beauty of this "apparently" trivial FIRST LAW. But we must remember that it took the genius of a Newton to first formulate it!
1 - A mass with two strings. We break the lower one OR the upper
one utilizing Newton.
2 - A HEAVY sphere is pulled upward on a string - first gently -
slowly — then suddenly - impulsively.
3 - A brick in the hand can be struck a severe blow and the hand
feels "NOTHING"!
4 - The mass of air on a sheet of paper has ENORMOUS INERTIA.
5 - A glass of water can be dragged along* gently on a piece of
paper but a sudden pull on the paper leaves the glass at rest. NOTE: The glass of water stays on the very edge of the table if its CENTER OF GRAVITY is NOT beyond the edge. See Program #1 on CENTER OF GRAVITY.
6 - A vehicle is at rest. It starts suddenly forward. Your head is
jerked backwards. NO! This is not right. Your head was at rest and it wishes to stay at rest! Now the vehicle is moving for¬ward. Suddenly it is brought to rest. YOU fly forward! Very dangerous!
7 - A pint of milk has greater inertia than a pint of cream. Milk Is
heavier than cream!
8 - A stack of coins stands erect - one atop another. The very bottom
one can be driven out with a sharp flat blade without troubling the others. This is a wonderful thing to do - you can even play it like a game. The STACK has great INERTIA and wishes to remain at rest.

D - A ball is whirled in a vertical circle on the end of a string. At the top of the path the ball is at this instant moving tangentially to the path -that is - in a straight line. If now we cut the string or let go of it what does the ball do? ANSWER: The ball goes off in the direction it was going - tangent to the circle. It does NOT fly out radially! Here we see the SECOND part of Newton's First Law beautifully demonstrated.

E - We show a likeness of Newton. The work of men must always be con¬nected with the men. In this way we acquire a warmer and deeper feeling for those who made these wonderful contributions to our Know¬ledge and Understanding.

### Course Description

Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.

This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.