Newton's Laws and Momentum

Sir Isaac Newton was instrumental in the world of physics towards the end of the seventeenth century and the way we can explain the everyday world is known as Newtonian Physics after him.

Newton's First Law

Newton's First Law states that a body will remain stationary or move at a constant velocity unless acted upon by a resultant force. I also show you a few examples including why the reaction/normal/contact force is not equal to the weight. 

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Newton's Second Law

F=ma is good but not always correct. A better definition of Newton's 2nd Law is to say that the force is directly proportional to the rate of change of momentum and acts in the same direction (this last part is really important). This covers examples where the mass or acceleration may not remain constant.

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Calculating Net Force and Acceleration

F=ma is a version of Newton's Second Law where the mass of an object is constant, and F represent the Net Force (or the Resultant Force). Here I show you a simple example where F is calculated allowing the acceleration to be worked out, I also talk about what happens when F = 0.

Newton's Third Law

Newton's 3rd Law: If object A exerts a force on object B, then object B exerts an equal and opposite force of the same type on object A (this is better than 'every action has an equal and opposite reaction'). This sounds simple but is what many people find difficult identifying in questions.

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Linear Momentum

Linear Momentum is defined as 'the product of an objects mass and velocity'. That's straightforward but why does momentum have the symbol 'p'? This video starts with the basics before we look at conservation of linear momentum in the next video.

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Conservation of Linear Momentum

How quickly does a pistol recoil when you fire it? You can calculate an answer by considering the conservation of momentum for a closed system.

The principle of conservation of momentum states that for a closed system the total momentum remains the same before and after a collision.

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Impulse (and how to get a straw through a potato)

When a force acts for a time it changes the momentum of an object. This is useful if you need to explain how an airbag in a car reduces the force on a person, or even how to get a straw through a potato! 

The impulse of a force is defined as the product of a force and the time for which it acts.

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Elastic and Inelastic Collisions

Momentum is always conserved and the total energy must remain constant but what about the kinetic energy?

For an elastic collision collision the total kinetic energy is conserved, when the collision is inelastic some of the kinetic energy is lost from the system while in a perfectly inelastic collision the two objects will stick together after the collision and move off together.

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