Newton’s Laws of MotionNewton’s Laws of Motion

Carl WozniakNorthern Michigan University

Carl WozniakNorthern Michigan University

Isaac NewtonIsaac Newton

Newton published the first work on theoretical physics, The Principia, in 1687.

In this, he showed us his principle of universal gravitation, as well as the rules guiding bodies in motion.

Newton published the first work on theoretical physics, The Principia, in 1687.

In this, he showed us his principle of universal gravitation, as well as the rules guiding bodies in motion.

Axiomato Sive Leges MotusAxiomato Sive Leges Motus

Corpus omne perseverari in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus illud a viribus impressis cogitur statum suum mutare.

Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur.

Actioni contratiam semper et aequalem esse reactionem: sive corporum duorum actiones in se mutuo semper esse aequades et in partes contraries dirigi.

Units of forceUnits of force

Units of force1 N = 1 kg * m/s2

The Newton is defined as the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s.

Units of force1 N = 1 kg * m/s2

The Newton is defined as the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s.

First law of motionFirst law of motion

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

First law of motionFirst law of motion

Objects tend to keep on doing what they're been doing.

These lead to the concepts of:Inertia: the resistance an object has to a

change in its state of motion.Momentum: mass in motion

P = m * v

Objects tend to keep on doing what they're been doing.

These lead to the concepts of:Inertia: the resistance an object has to a

change in its state of motion.Momentum: mass in motion

P = m * v

First law of motionFirst law of motion

Seeing the first law every day blood rushes from your head to your feet while quickly stopping

when riding on a descending elevator. the head of a hammer can be tightened onto the wooden handle by

banging the bottom of the handle against a hard surface. to dislodge ketchup from the bottom of a ketchup bottle, it is often

turned upside down and, thrust downward at high speeds and then abruptly halted.

headrests are placed in cars to prevent whiplash injuries during rear-end collisions.

while riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or rock or other object which abruptly halts the motion of the skateboard.

Seeing the first law every day blood rushes from your head to your feet while quickly stopping

when riding on a descending elevator. the head of a hammer can be tightened onto the wooden handle by

banging the bottom of the handle against a hard surface. to dislodge ketchup from the bottom of a ketchup bottle, it is often

turned upside down and, thrust downward at high speeds and then abruptly halted.

headrests are placed in cars to prevent whiplash injuries during rear-end collisions.

while riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or rock or other object which abruptly halts the motion of the skateboard.

Second law of motionSecond law of motion

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Boiled down, this gives us one of the most famous equations in physics.

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Boiled down, this gives us one of the most famous equations in physics.

Second law of motionSecond law of motion

F = maF = maForce = mass X acceleration

Second law of motionSecond law of motion

So what is acceleration?the rate at which an object changes its

velocity.

So what is velocity?the rate at which an object changes its

position

Um…that sounds like speed.

So what is acceleration?the rate at which an object changes its

velocity.

So what is velocity?the rate at which an object changes its

position

Um…that sounds like speed.

Second law of motionSecond law of motion

And they are very close. Speed, however, is a scalar quantity, and velocity is a vector quantity.

Ah…now I don’t understand at all.Scalars are quantities which are fully

described by a magnitude alone. Vectors are quantities which are fully

described by both a magnitude and a direction.

And they are very close. Speed, however, is a scalar quantity, and velocity is a vector quantity.

Ah…now I don’t understand at all.Scalars are quantities which are fully

described by a magnitude alone. Vectors are quantities which are fully

described by both a magnitude and a direction.

Second law of motionSecond law of motion

Is it too late to drop this class?Here’s an example:

If you’re in your car going 60 mphThat’s your speed

If you’re in your car traveling north at 60 mphThat’s your velocity

Is it too late to drop this class?Here’s an example:

If you’re in your car going 60 mphThat’s your speed

If you’re in your car traveling north at 60 mphThat’s your velocity

Second law of motionSecond law of motion

Think of speed and velocity as how fast something is moving

Acceleration then, is a change in how fast something is moving over a given period of time

Remember though, forces don’t cause motion, they only cause accelerations Force is not needed to keep an object in

motion

Think of speed and velocity as how fast something is moving

Acceleration then, is a change in how fast something is moving over a given period of time

Remember though, forces don’t cause motion, they only cause accelerations Force is not needed to keep an object in

motion

Third law of motionThird law of motion

Newton’s third law of motion is perhaps the best known: For every action there is an equal but

opposite reactionThis might seem simple, but let’s see if

you understand

Newton’s third law of motion is perhaps the best known: For every action there is an equal but

opposite reactionThis might seem simple, but let’s see if

you understand

Third law of motionThird law of motion

While driving down the road, an unfortunate bug strikes the windshield of a bus. Quite obviously, this is a case of Newton's third law of motion. The bug hit the bus and the windshield hit the bug. Which of the two forces is greater: the force on the bug or the force on the bus?

While driving down the road, an unfortunate bug strikes the windshield of a bus. Quite obviously, this is a case of Newton's third law of motion. The bug hit the bus and the windshield hit the bug. Which of the two forces is greater: the force on the bug or the force on the bus?

Third law of motionThird law of motion

While driving down the road, an unfortunate bug strikes the windshield of a bus. Quite obviously, this is a case of Newton's third law of motion. The bug hit the bus and the windshield hit the bus. Which of the two forces is greater: the force on the bug or the force on the bus?

While driving down the road, an unfortunate bug strikes the windshield of a bus. Quite obviously, this is a case of Newton's third law of motion. The bug hit the bus and the windshield hit the bus. Which of the two forces is greater: the force on the bug or the force on the bus?

The forces are identical. Why does the bug splatter? It has less mass.

Third law of motionThird law of motion A gun recoils when it is fired. The recoil is

the result of action-reaction force pairs. As the gases from the gunpowder explosion expand, the gun pushes the bullet forwards and the bullet pushes the gun backwards. The acceleration of the recoiling gun is ... a. greater than the acceleration of the bullet. b. smaller than the acceleration of the bullet. c. the same size as the acceleration of the

bullet.

A gun recoils when it is fired. The recoil is the result of action-reaction force pairs. As the gases from the gunpowder explosion expand, the gun pushes the bullet forwards and the bullet pushes the gun backwards. The acceleration of the recoiling gun is ... a. greater than the acceleration of the bullet. b. smaller than the acceleration of the bullet. c. the same size as the acceleration of the

bullet.

Third law of motionThird law of motion A gun recoils when it is fired. The recoil is

the result of action-reaction force pairs. As the gases from the gunpowder explosion expand, the gun pushes the bullet forwards and the bullet pushes the gun backwards. The acceleration of the recoiling gun is ... a. greater than the acceleration of the bullet. b. smaller than the acceleration of the bullet. c. the same size as the acceleration of the

bullet.

A gun recoils when it is fired. The recoil is the result of action-reaction force pairs. As the gases from the gunpowder explosion expand, the gun pushes the bullet forwards and the bullet pushes the gun backwards. The acceleration of the recoiling gun is ... a. greater than the acceleration of the bullet. b. smaller than the acceleration of the bullet. c. the same size as the acceleration of the

bullet.

The force on the gun equals the force on the bullet. Yet, acceleration depends on both force and mass. The bullet has a greater acceleration due to the fact that it has a smaller mass.

Graphing movementGraphing movement

We graph movement with the P-T graph Position vs. time

We graph movement with the P-T graph Position vs. time

Car moving at constant velocity

Graphing movementGraphing movement

We graph movement with the P-T graph Position vs. time

We graph movement with the P-T graph Position vs. time

Car accelerating

Graphing movementGraphing movement

The shape of the graph tells you what is going on.

The shape of the graph tells you what is going on.

Moving right, constant velocity, fast

Moving right, constant velocity, slow

Moving left, constant velocity, slow

Moving left, constant velocity, fast

Moving left, slow to fast

Moving left, fast to slow

Graphing movementGraphing movement

What are these two doing?What are these two doing?

Graphing movementGraphing movement

What are these two doing?What are these two doing?

•A is moving to the right and accelerating

•B is moving to the left and accelerating