Chapter 4Chapter 4Newton’s 1Newton’s 1stst Law Law

Aristotle – Believed that in order for an Aristotle – Believed that in order for an object to move, a force had to be object to move, a force had to be pushing it.pushing it.

“All objects have a natural state of rest.Heavy things have a natural state on The ground, and very light things have A natural state in the air, such as smoke.”

How do you think Aristotle explained the Stars and planets that move every night?

How would Aristotle view a ball How would Aristotle view a ball rolling across the table and slowly rolling across the table and slowly

coming to a stop?coming to a stop?

A)A) Friction makes the ball stopFriction makes the ball stop

B)B) The ball wants to come to its “natural” The ball wants to come to its “natural” resting stateresting state

C)C) Gravity makes the ball stopGravity makes the ball stop

How would Galileo say the ball stopped?How would Galileo say the ball stopped?

Galileo GalileeGalileo Galilee

Galileo’s experiments:Galileo’s experiments:

Galileo’s ideasGalileo’s ideas

Through his experiments, objects in motion Through his experiments, objects in motion want to stay in motion, the reason objects want to stay in motion, the reason objects come to rest is because of friction. come to rest is because of friction. Friction is the force that opposes motion.Friction is the force that opposes motion.

Friction put a wrench in his calculations on motion – he Friction put a wrench in his calculations on motion – he needed a new form of math – Calculus needed a new form of math – Calculus

Coincidentally, Galileo’s views on motion were taken with a lot Coincidentally, Galileo’s views on motion were taken with a lot of criticism. Aristotle’s views had been accepted for 2000 of criticism. Aristotle’s views had been accepted for 2000 years – how could Galileo be “smarter” than Aristotle???years – how could Galileo be “smarter” than Aristotle???

How does friction work?How does friction work?

Friction from the microscopic level:Friction from the microscopic level:

Newton’s 1Newton’s 1stst Law Law

At age 24, Isaac Newton came up with At age 24, Isaac Newton came up with his world changing 3 laws of motion. his world changing 3 laws of motion.

The first:The first:

An object at rest will stay at rest and An object at rest will stay at rest and an object in motion will stay in an object in motion will stay in motion unless a force acts upon it.motion unless a force acts upon it.

Concept QuizConcept Quiz

If the force of gravity between the If the force of gravity between the planets and the sun were to planets and the sun were to suddenly disappear, what path would suddenly disappear, what path would they follow?they follow?

A

B

C

D

InertiaInertiaInertia – an objects resistance to changeInertia – an objects resistance to change

Newton’s 1Newton’s 1stst law is sometimes referred to law is sometimes referred to the law of inertia.the law of inertia.

A measure of inertia = massA measure of inertia = mass

Which has the most inertia?Which has the most inertia?A) An empty canA) An empty can B) Can full of waterB) Can full of waterC) Can full of sandC) Can full of sand D) Can full of a D) Can full of a

vacuumvacuum

Concept QuizConcept QuizWill it be just as difficult to shake a Will it be just as difficult to shake a

bowling ball in space as it is on bowling ball in space as it is on earth?earth?

A)A) YesYes

B)B) NoNo

Will it be just as easy to “wind up” a bowling ball in space?

Does a 2 kg bunch of bananas have 2 times as much inertia as a 1 kg block of steel?

Mass vs WeightMass vs Weight

Mass is different than weightMass is different than weight

Mass is the measure of matter in an Mass is the measure of matter in an object (the number and type of object (the number and type of atoms). This is measured with a atoms). This is measured with a balance.balance.

Concept QuizConcept Quiz

Will you have the same mass on the Will you have the same mass on the moon?moon?

A)A) YesYes

B)B) NoNo

WeightWeight

Weight is the force of gravity on an Weight is the force of gravity on an object. object.

It is measured with spring scales. A It is measured with spring scales. A scale will compress due to gravity.scale will compress due to gravity.

WeightWeight

Weight is a force. It is measured by taking Weight is a force. It is measured by taking the mass of an object multiplied by the mass of an object multiplied by gravity.gravity.

Weight (N) = mass (kg) x gravity (m/sWeight (N) = mass (kg) x gravity (m/s²)²)

The SI unit for weight is the Newton.The SI unit for weight is the Newton.

(One Newton is equal to about a ¼ burger)(One Newton is equal to about a ¼ burger)

Concept QuizConcept Quiz

If a persons mass is 70 kg, about how If a persons mass is 70 kg, about how much do they weigh? much do they weigh?

A)A) 70 kg70 kg

B)B) 70 N70 N

C)C) 140 N140 N

D)D) 700 N700 N

E)E) 1400 N1400 N