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Newton’s Laws

Discover Newton's laws of motion and learn how objects move based on concepts like mass and force. Explore examples of forces, units of force, and the relationship between force, acceleration, and mass. Gain insights into action and reaction forces and how they interact with different objects.

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Newton’s Laws

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  1. Newton’s Laws

  2. Explaining motion Isaac Newton was the first person to explain WHY objects move the way they do. He based his laws of motion on two key concepts: • mass • force

  3. What is mass? All matter has mass and takes up space. A solid rock has mass. So do gases and liquids. With your hand out the window of a moving car, you feel the mass in the air pushing against you.

  4. Types of forces The concept of force: A force is a push or a pull. Forces can cause an object to change its motion. Can you give some examples of forces? Examples of forces: • weight • friction • tension from rope • force from a spring • electric force

  5. Units of force Quantitative: Force is measured in newtons.

  6. Newton’s first law The first law has two parts. The second part is not so obvious.

  7. Understanding the first law Motion only changes through the action of a net force. If the net force is zero – there can be no changes in motion.

  8. The law of inertia Newton’s first law is also known as the law of inertia. • Inertia is the tendency of an object to resist changes in the speed or direction of its motion. • The inertia of an object is related to its mass. • The more massive an object is, the more inertia it has, and the more it will resist having its motion changed.

  9. The meaning of the second law Net force (N) Acceleration(m/s2) Mass (kg) Velocity must change if a net force acts on an object. According to the second law, a net force on an object causes it to accelerate. If an object accelerates, its velocity must change.

  10. The meaning of the second law Net force (N) Acceleration(m/s2) Mass (kg) The net force is zero on an object with constant velocity. If velocity stays constant, then the acceleration is zero—so the net force must also be zero. This does NOT necessarily mean there is no motion!

  11. Direction of force and acceleration Acceleration and force are vectors.

  12. Units The second law can help you remember the definition of a newton. Always use mass in kilograms and acceleration in m/s2 when applying Newton’s second law.

  13. Applying Newton’s second law If you know the force on an object, you can predict changes in its motion. If you know the acceleration of an object, you can determine the net force on it.

  14. Finding motion from forces If you know the force on an object, you can predict changes in its motion. A 0.25 kg ball is traveling 40 m/s to the right when it is hit with a force of 3,000 N for 0.005 seconds. What is its final velocity?

  15. Steps A 0.25 kg ball is traveling 40 m/s to the right when it is hit with a force of 3,000 N for 0.005 seconds. What is its final velocity? • Use force and mass to find acceleration through the second law. • Use the acceleration to find the change in velocity or position.

  16. Solution A 0.25 kg ball is traveling 40 m/s to the right when it is hit with a force of 3,000 N for 0.005 seconds. What is its final velocity? • Use force and mass to find acceleration through the second law. Impacts can cause very large accelerations for short times!

  17. Solution A 0.25 kg ball is traveling 40 m/s to the right when it is hit with a force of 3,000 N for 0.005 seconds. What is its final velocity? • Use force and mass to find acceleration through the second law. • Use the acceleration to find the change in velocity or position. The ball reverses direction!

  18. Action and reaction forces Action Forces always come in pairs. If one object puts a force on a second object, the second object always puts an equal and opposite force back on the first object. Newton’s third law: For every action (force) there is always an equal and opposite reaction (force).Newton’s third law is a law of interactions between objects. Reaction

  19. There are always two objects Action: racquet pushes on ball. Reaction: ball pushes back on racquet. Action-reaction forces always act on different objects: One force acts on the racquet. Its partner force acts on the ball.

  20. Free-body diagrams Action: racquet pushes on ball. Reaction: ball pushes back on racquet. Only one of these forces appears on an object’s free-body diagram: the force that acts ON the object.

  21. Force pairs don’t cancel out Action-reaction pairs don’t cancel out because they always act on different objects: • One force acts on the racquet. • Its partner force acts on the ball. Only forces that act on the same object can cancel each other out.

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