Chapter 4 Newton’s 1 st Law Aristotle – Believed that in order for an object to move, a force had to be 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 rolling across the table and slowly coming to a stop? A) Friction makes the ball stop B) The ball wants to come to its “natural” resting state C) Gravity makes the ball stop How would Galileo say the ball stopped?

Galileo Galilee Galileo’s experiments:

Galileo’s ideas Through his experiments, objects in motion want to stay in motion, the reason objects come to rest is because of friction. Friction is the force that opposes motion. Friction put a wrench in his calculations on motion – he needed a new form of math – Calculus Coincidentally, Galileo’s views on motion were taken with a lot of criticism. Aristotle’s views had been accepted for 2000 years – how could Galileo be “smarter” than Aristotle???

How does friction work? Friction from the microscopic level:

Newton’s 1 st Law At age 24, Isaac Newton came up with his world changing 3 laws of motion. The first: An object at rest will stay at rest and an object in motion will stay in motion unless a force acts upon it.

Concept Quiz If the force of gravity between the planets and the sun were to suddenly disappear, what path would they follow? If the force of gravity between the planets and the sun were to suddenly disappear, what path would they follow? A B C D

Inertia Inertia – an objects resistance to change Newton’s 1 st law is sometimes referred to the law of inertia. A measure of inertia = mass Which has the most inertia? A) An empty canB) Can full of water C) Can full of sandD) Can full of a vacuum

Concept Quiz Will it be just as difficult to shake a bowling ball in space as it is on earth? A) Yes B) No 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 Weight Mass is different than weight Mass is the measure of matter in an object (the number and type of atoms). This is measured with a balance.

Concept Quiz Will you have the same mass on the moon? A) Yes B) No

Weight Weight is the force of gravity on an object. It is measured with spring scales. A scale will compress due to gravity.

Weight Weight is a force. It is measured by taking the mass of an object multiplied by gravity. Weight (N) = mass (kg) x gravity (m/s²) Weight (N) = mass (kg) x gravity (m/s²) The SI unit for weight is the Newton. (One Newton is equal to about a ¼ burger)

Concept Quiz If a persons mass is 70 kg, about how much do they weigh? A) 70 kg B) 70 N C) 140 N D) 700 N E) 1400 N