Newton’s Newton’s Laws of Laws of MotionMotion

Sir Isaac Newton was an English scientist Sir Isaac Newton was an English scientist and mathematician famous for his and mathematician famous for his discovery of the law of gravity also discovery of the law of gravity also discovered the three discovered the three laws of motionlaws of motion.He .He was born in the year 1643 on january 4was born in the year 1643 on january 4thth and expired on march 31th, 1727.and expired on march 31th, 1727. He He published about laws of motion & laws of published about laws of motion & laws of gravity in his book gravity in his book Philosophiae Naturalis Philosophiae Naturalis Principia MathematicaPrincipia Mathematica in 1687. in 1687. Today Today these laws are known as these laws are known as Newton’s Laws of Newton’s Laws of MotionMotion..

INTRODUCTION OF INTRODUCTION OF NEWTONNEWTON

Newton’s Laws of MotionNewton’s Laws of Motion

11stst Law Law – An object at rest will stay – An object at rest will stay at rest, and an object in motion will at rest, and an object in motion will stay in motion at constant velocity, stay in motion at constant velocity, unless acted upon by an unless acted upon by an unbalanced force.unbalanced force.

22ndnd Law Law – – Force equals mass times Force equals mass times acceleration.acceleration.

33rdrd Law Law – – For every action there is For every action there is an equal and opposite reactionan equal and opposite reaction..

Newton’s First LawNewton’s First Law

An object at rest tends to An object at rest tends to stay at rest and an object in stay at rest and an object in motion tends to stay in motion motion tends to stay in motion unless acted upon by an unless acted upon by an unbalanced force.unbalanced force.

WWhat does this hat does this mean?mean?

Basically, an object will “keep doing Basically, an object will “keep doing what it was doing” unless acted on by what it was doing” unless acted on by an unbalanced force.an unbalanced force.

If the object was sitting still, it will If the object was sitting still, it will remain stationaryremain stationary. If it was moving at . If it was moving at a constant velocity, it will a constant velocity, it will keep keep movingmoving..

It takes It takes forceforce to change the motion of to change the motion of an object.an object.

11stst Law Law Inertia is the Inertia is the

tendency of an tendency of an object to resist object to resist changes in its changes in its velocity: velocity: whether in whether in motion or motion or motionless.motionless.

These pumpkins will not move unless acted on by an unbalanced force.

Some Examples from Real Some Examples from Real LifeLife

Two teams are playing tug of war. They Two teams are playing tug of war. They are both exerting equal force on the rope are both exerting equal force on the rope in opposite directions. This balanced in opposite directions. This balanced force results in no change of motion.force results in no change of motion.

A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

Newton’s Second LawNewton’s Second Law

Force equals mass times acceleration.Force equals mass times acceleration.

F = maF = ma

Acceleration: a measurement of how quickly an object is changing speed.

If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.

What does F = ma mean?What does F = ma mean?Force is Force is directly proportionaldirectly proportional to mass and acceleration. to mass and acceleration. Imagine a ball of a certain mass moving at a certain Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force. acceleration. This ball has a certain force.

Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball.

Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.

Newton’s Third LawNewton’s Third Law

For every action there is an For every action there is an equal and opposite reaction.equal and opposite reaction.

What does this mean?What does this mean?

For every force acting on an object, there is an equal force acting in the opposite direction. Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force. This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up.

33rdrd Law Law

There are two forces There are two forces resulting from this resulting from this interaction - a force on interaction - a force on the chair and a force on the chair and a force on your body. These two your body. These two forces are called forces are called actionaction and and reactionreaction forces. forces.

33rdrd Law LawThe reaction of a rocket The reaction of a rocket is an application of the is an application of the third law of motion. third law of motion. Various fuels are burned Various fuels are burned in the engine, producing in the engine, producing hot gases. hot gases.

The hot gases push The hot gases push against the inside tube of against the inside tube of the rocket and escape out the rocket and escape out the bottom of the tube. the bottom of the tube. As the gases move As the gases move downward, the rocket downward, the rocket moves in the opposite moves in the opposite direction.direction.

VocabularyVocabularyInertia:

the tendency of an object to resist changes in its state of motion

Acceleration:

•a change in velocity

•a measurement of how quickly an object is changing speed, direction or bothVelocity:

The rate of change of a position along a straight line with respect to time Force:

strength or energy