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Newton’s 1 st Law of motion

Newton’s 1 st Law of motion. Law of inertia. Newton’s first law of motion. An object at rest will stay at rest and an object in motion will continue in motion with the same speed and direction unless acted on by a force . aka – Law of Inertia. What does this mean?.

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Newton’s 1 st Law of motion

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  1. Newton’s 1st Law of motion Law of inertia

  2. Newton’s first law of motion • An object at rest will stay at rest and an object in motion will continue in motion with the same speed and direction unless acted on by a force. • aka – Law of Inertia

  3. What does this mean? Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force. If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving. It takes force to change the motion of an object.

  4. Some Examples from Real Life • A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion. Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

  5. Force • Force • A push or pull • Any action that has the ability to change motion. • Units = newtons (N) • There can be no change in motion without the presence of a force.

  6. Inertia • Inertia: • the tendency of an object to resist changes in its state of motion • Objects with more mass have more inertia = more resistant to changes in motion

  7. Mass vs. weight • Mass: • The amount of matter contained in an object • Units: kilograms (kg) • Weight: • The gravitational force of an object • Units = newtons (N) The weight of an object is proportional to its mass!

  8. What is a newton? • One Newton = amount of force needed to cause a mass of one kilogram to speed up by 1.0 m/s/s. • 1.0 pound = 4.448 N • One pound is force exerted by gravity on a mass of 0.454 kg.

  9. Calculating weight W = m·g W = weight (N) m = mass (kg) g = acceleration due to gravity = 9.80m/s2

  10. Examples of weight problems • What is the weight of each of the following objects? • 0.113 kg hockey puck • 108 kg football player • 871 kg automobile Answers: • 1.11 N • 1060 N • 8540 N

  11. More Examples 2. Find the mass, in kilograms, of each of these weights. • 95 N • 82 N • 0.98 N Answers: • 9.7 kg • 8.4 kg • 0.10 kg

  12. If objects in motion tend to stay in motion, why don’t moving objects keep moving forever? • Things don’t keep moving forever because there’s almost always an unbalanced force acting upon it. • A book sliding across a table slows down and stops because of the force of ___________. • If you throw a ball upwards it will eventually slow down and fall because of the force of _____________.

  13. In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever.

  14. What is Friction? • The force that results from the relative motion between objects that are in contact. • Example: • The tire and the road • Ice skate and ice surface • Air resistance Friction between sled and snow surface

  15. Net Force • Net Force = total of all forces acting on an object. • Dependent on the amount of forces and the direction of the forces. • Balanced Forces: • Net force equals zero (forces are equal but opposite). • No change in motion of object • Unbalanced Forces: • Net force does not equal zero. • Results in change on motion on object.

  16. Examples

  17. Drawing Net Force Diagrams • What is the net force on the truck? 100 N – 60 N = 40 N right Use arrows to display the direction and magnitude of the force being applied!

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