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Newton’s Second Law

Newton’s Second Law. But first… Review: Newton’s First Law. If an object experiences NO net force…. Resting objects remain at rest. Moving objects move at a constant velocity. Newton’s First Law. Also known as the Law of Inertia

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Newton’s Second Law

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  1. Newton’s Second Law

  2. But first…Review: Newton’s First Law If an object experiences NO net force…. • Resting objects remain at rest. • Moving objects move at a constant velocity.

  3. Newton’s First Law • Also known as the Law of Inertia Inertia: An object’s tendency to keep on doing what it’s already doing.

  4. Newton’s First Law Inertia: An object’s tendency to keep on doing what it’s already doing. An object at rest will remain at rest…

  5. Law of Inertia:An object in motion will continue in motion…

  6. Inertia • Inertia is a term used to measure the ability of an object to resist a change in its state of motion. • An object with a lot of inertia takes a lot of force to start or stop; an object with a small amount of inertia requires a small amount of force to start or stop. • The word “inertia” comes from the Latin word inertus, which can be translated to mean “lazy.”

  7. Inertia • Inertia is a term used to measure the ability of an object to resist a change in its state of motion. • Mass is a measure of inertia. The higher the mass of an object is, the more it resists changes to its motion:

  8. Law of inertia:(click here) • The law of inertia and YOU!

  9. Equilibrium • The condition of zero acceleration is called equilibrium. • In equilibrium, all forces cancel out leaving zero net force. • Objects that are standing still are in equilibrium because their acceleration is zero. • Objects that are moving at constant speed and direction are also in equilibrium. • A static problem usually means there is no motion.

  10. Calculate force • A woman is holding two dogs on a leash. • If each dog pulls with a force of 80 newtons, how much force does the woman have to exert to keep the dogs from moving?

  11. Newton’s Second Law The acceleration of an object is: • Directly proportional to the net force acting on it, and… • Inversely proportional to its mass

  12. What does that mean? The acceleration of an object is: • Directly proportional to the net external force acting on it (The stronger the force applied to an object, the greater the acceleration will be.) • Inversely proportional to its mass (The heavier the object, the less it will accelerate for a given force.)

  13. Newton's Second Law • If you apply more force to an object, it accelerates at a higher rate.

  14. Newton's Second Law • If an object has more mass, it accelerates at a lower rate because it has more inertia.

  15. Practice: Calculating acceleration • A cart rolls down a ramp. • The cart has a mass of 500 grams (0.5 kg). • Using a spring scale, you measure a net force of 2 newtons pulling the car down. • Calculate the acceleration of the cart.

  16. Calculating acceleration • Three people are pulling on a wagon applying forces of 100 N,150 N, and 200 N. • The wagon has a mass of 25 kilograms. • Determine the acceleration and the direction the wagon moves.

  17. Calculating force • An airplane needs to accelerate at 5 m/sec2 to reach take-off speed before reaching the end of the runway. • The mass of the airplane is 5,000 kilograms. • How much force is needed from the engine?

  18. More on weight…. • Weight (as you know) is a force. • Weight is the force exerted on an object by gravity. • The magnitude of weight is found by Newton’s Second Law: F = m x a Weight = mass x (9.8 m/s2)

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