# When I am holding a weight on a rope, what is the evidence that the forces cancel to zero?

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When I am holding a weight on a rope, what is the evidence that the forces cancel to zero?

Notes: Wednesday, October 10, 2012 Topic: Inertia EQ: Why is a heavier shopping cart harder to push?

Key Definitions Inertia The property of a body, or object, to resist change to its state of motion. Friction The name given to the force that acts between materials that touch as they move past one another.

Newton’s First Law Every object continues in a state of rest, or of uniform speed in a straight line, unless acted upon by an nonzero net force.

Things to think about – Objects continue to move by themselves. – Forces are needed to overcome any friction that may be present and to set objects in motion initially. – Once the object is moving in a force-free environment, it will move in a straight line indefinitely.

think! A force of gravity between the sun and its planets holds the planets in orbit around the sun. If that force of gravity suddenly disappeared, in what kind of path would the planets move?

Mass A measure of the inertia, or “laziness,” that an object exhibits in response to any effort made to start it, stop it, or otherwise change its state of motion.

Don’t confuse yourself! Don’t confuse mass with volume. Volumes is a measure of the amount of space an object takes up. Don’t confuse mass with weight. Weight is gravitational force on an object.

Measuring Mass Mass is measured in kilograms. The rest of the world measures people in kilograms. Weight is not mass, but Americans measure themselves with weight. Measuring Force Force is measured in Newton’s. One newton is equal to about 0.25 pounds. One kilogram of mass has 10 Newtons of weight force.

think! Does a 2-kilogram bunch of bananas have twice as much inertia as a 1- kilogram loaf of bread? Twice as much mass? Twice as much volume? Twice as much weight, when weighed in the same location?

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