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Motion and Force

Motion and Force. Chapter Twelve: Distance, Time, and Speed Chapter Thirteen: Forces Chapter Fourteen: Force and Motion. Chapter Thirteen: Forces. 13.1 Forces 13.2 Addition of Forces. Investigation 13A. Forces. What is force and how is it measured?. 13.1 The cause of forces.

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Motion and Force

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  1. Motion and Force • Chapter Twelve: Distance, Time, and Speed • Chapter Thirteen: Forces • Chapter Fourteen: Force and Motion

  2. Chapter Thirteen: Forces • 13.1 Forces • 13.2 Addition of Forces

  3. Investigation 13A Forces • What is force and how is it measured?

  4. 13.1 The cause of forces • A force is a push or pull, or any action that has the ability to change motion. • The key word here is action, force is an action.

  5. 13.1 The cause of forces • Fundamentally, forces come from the interaction between atoms and energy.

  6. 13.1 Units of force • When you measure weight in pounds on a scale, you are measuring the force of gravity acting on the object. • The word “pound” comes from the Latin word pondus, which means “weight.”

  7. 13.1 The cause of forces • One pound of force equals 4.48 newtons.

  8. 13.1 Gravity and weight • The force of gravity on an object is called weight. • Mass and weight are not the same thing!

  9. 13.1 Gravity and weight • A 10-kilogram rock has a mass of 10 kilograms no matter where it is in the universe. • A 10-kilogram rock’s weight however, can vary greatly depending on where it is.

  10. 13.1 Calculating weight • The weight equation can be rearranged into three forms to calculate weight, mass, or the strength of gravity.

  11. 13.1 Friction • Frictionis a force that resists the motion of objects or surfaces. • Many kinds of friction exist.

  12. 13.1 Friction • Friction depends on both of the surfaces in contact. • When the hockey puck slides on ice, a thin layer of water between the rubber and the ice allows the puck to slide easily.

  13. 13.1 Identifying friction forces • Friction is a force, measured in newtons just like any other force. • Static frictionkeeps an object at rest from moving.

  14. 13.1 Identifying friction forces • Sliding frictionis a force that resists the motion of an object moving across a surface.

  15. 13.1 A model for friction • The greater the force squeezing two surfaces together, the greater the friction force.

  16. 13.1 Reducing the force of friction • Unless a force is constantly applied, friction will slow all motion to a stop eventually. • It is impossible to completely get rid of friction, but it can be reduced.

  17. 13.1 Reducing the force of friction • The friction between a shaft (the long pole in the picture) and an outer part of a machine produces a lot of heat. • Friction can be reduced by placing ball bearings between the shaft and the outer part.

  18. 13.1 Useful friction • Friction is also important to anyone driving a car. • Grooved tire treads allow space for water to be channeled away from the road-tire contac point, allowing for more friction in wet conditions.

  19. 13.1 Useful friction • Shoes are designed to increase the friction between their soles and the ground. Why do you think these shoes increase friction? • Players wearing cleats can apply much greater forces against the ground to help them move and to keep from slipping.

  20. Activity Kilograms to Newtons: Make your own Measurements! • The unit for measuring force called the newton is named after Sir Isaac Newton. • In the activity below you will explore the concept of a newton.

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