Newtons laws of motion
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Newtons Laws of Motion. 1 st & 2 nd Laws. Newton’s First Law. Unbalanced forces. I f there are no forces acting or if the forces acting on an object are balanced, the object will keep doing what it was already doing.

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Newtons Laws of Motion

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Newtons laws of motion

Newtons Laws of Motion

1st & 2nd Laws


Newtons laws of motion

Newton’s First Law


Unbalanced forces

Unbalanced forces

If there are no forces acting or if the forces acting on an object are balanced, the object will keep doing what it was already doing.

If the object is stationary, it will remain stationary; if it is moving at a constant speed, it will continue travelling at this speed (not speeding up or slowing down).

This statement is called Newton’s first law of motion, which is also known as the law of inertia.


Newtons laws of motion

All objects possess inertia, which means a tendency to resist change.

The larger the mass of an object, the harder it is to change its motion because it possesses more inertia than an object with a smaller mass. This is why it is much easier to stop an empty runaway shopping trolley than a full one.


Interactive activity

Interactive activity

D:\int\nwtLaws.exe


Newtons laws of motion

Newton’s Second Law


Newtons laws of motion

Describes how an object will move when it is acted upon by unbalanced forces.

A force is a push or a pull that causes a change in motion.

A change in motion is acceleration.

The size of a force is measured in newtons (symbol N). Some common measures of force are:

  • switching a light switch, 5 N

  • removing a ring tab from a can, 20 N

  • hitting a tennis ball with a racquet, 2000 N

  • the force of a jet engine, 200 000 N


Newtons laws of motion

A body will accelerate in the direction of the overall force that acts upon it.

The size of this acceleration depends on the mass of the object and the size of the force acting.

This relationship can be expressed as:

F = ma

Force is measured in newtons, mass is measured in kilograms and acceleration is measured in metres per second squared.


Newtons laws of motion

So using the equation;

  • if you double the acceleration rate and the mass remains the same what happens to the force?

  • If you triple the acceleration rate and the mass remains the same what happens to the force?

  • If you double the mass and the acceleration rate is the same what happens to the force?

  • If you halve the mass and acceleration rate remains the same what happens to the force?

  • If you double the force and the mass remains the same what happens to the acceleration rate?


Newtons laws of motion

If we rearrange this formula, we can express acceleration as:


Examples

Examples:

A car of mass 1200 kg that travels to the right, with a driving force of 3000 N, along a surface that provides a 600 N frictional force will experience a net force of:

.... So it will travel with an acceleration of:

A boy of mass 50 kg coasting along on a skateboard to the left, with a frictional force of 450 N, will experience an acceleration of:


Newtons laws of motion

Isaac Newton’s second law of motion:‘A large force produces a large acceleration, provided that the mass remains the same. A large mass reduces the acceleration of the same force’.


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