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Newton’s 1 st Law

Newton’s 1 st Law. Mrs. Kiley 8 th Grade Science. Newton’s First Law of Motion is also called the Law of Inertia. A restatement of Galileo’s ideas about forces not needed to keep an object moving. .

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Newton’s 1 st Law

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  1. Newton’s 1st Law Mrs. Kiley 8th Grade Science

  2. Newton’s First Law of Motion is also called the Law of Inertia. • A restatement of Galileo’s ideas about forces not needed to keep an object moving.

  3. Newton’s 1st Law states that every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force. • Also commonly stated: objects at rest tend to stay at rest, objects in motion tend to stay in motion.

  4. Objects at Rest • Things tend to keep on doing what they’re already doing. • Dishes on a table are in a state of rest – they will remain at rest unless a force acts on them. • Example: pulling a tablecloth out from under a table full of dishes. http://www.youtube.com/watch?v=KcSwxT_z6io

  5. Objects in Motion • Hockey Puck example: • If you slid a hockey puck along the surface of a street, how far would it go? • Compare that to an ice rink. How far would it go? • Why the difference?

  6. In the absence of forces, a moving object tends to move in a straight line indefinitely. • It is a VERY common misconception that forces must continue to be present for an object to continue moving. • Ancient people thought this and many people today still believe this.

  7. Forces are needed to overcome any friction that maybe present and set objects in motion initially. • Once the object is moving, it will move in a straight line by virtue of its own inertia.

  8. Mass as a Measure of Inertia • Kick an empty can – what happens? • Kick a can filled with sand – what happens? • Kick a can filled with steel nails – what happens? • The nail filled can has much more inertia than the other two cans.

  9. The amount of inertia an object has depends on its mass. • The more mass an object has, the greater its inertia and the more force it takes to change its state of motion. • Pushing a refrigerator…

  10. Mass is Not Volume • Mass and volume are not the same thing. • Volume is a measure of space and measured in units such as cubic centimeters and liters. • Mass is measured in the unit of kilograms. • For instance, equal size bags of cotton and nails have equal volumes but very different masses.

  11. Which object has greater inertia?

  12. Mass is Not Weight • Mass and weight are often confused, but are not the same thing. • Mass is a measure of the amount of material in an object and depends only on the number of and kind of atoms that compose it. • Weight is a measure of the gravitational force acting on the object. Weight depends on the object’s location.

  13. Mass is Inertia • Mass is the quantity of matter in an object. • Mass is a measure of the inertia that an object exhibits in response to any effort to make it start, stop, or otherwise change its state of motion. • Weight is the force of gravity on an object.

  14. Summary • Newton’s 1st Law is often called the Law of Inertia. • Inertia is an object’s tendency to resist a change in motion. • Objects at rest tend to stay at rest; objects in motion tend to stay in motion. • Mass is not the same thing as volume or weight.

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