Newton’s 3 Laws

Meet Galileo Just a few accomplishment… – Discovered Heliocentric solar system – Phases of Venus and Mercury – Jupiter's moons – Acceleration of Earth’s gravity is a constant – Most importantly for us: proposed that a net force was only needed to start, stop, or change the direction of an object

Meet Sir Isaac Newton Just a few accomplishments… – Calculus – Worked with Kepler on orbits of planets – Color Theory – Quantifying gravity This leads to his 3 laws

Newton’s 1 st law An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force

Inertia Newton’s 1 st law is also called the law of Inertia Galileo actually thought of the idea Inertia is the tendency of an object to resist a change in motion Inertia is not a force, it is a physical property of matter!

Inertia is property of mass More mass = more inertia A full bucket is harder to move than an empty bucket: this is because of inertia

Newton’s 2 nd law It is a formula: in fact it is the most important relationship in all of physics Practice on page 53, 1-2

Examples of Newton’s Second Law

What does it mean? The greater the net force: the greater the acceleration The greater the mass: the smaller the acceleration If the mass of a rock is doubled, how would this effect acceleration if the force does not change?

Newton’s 3 rd Law If object A exerts a force on object B, object B will exert a force on object A that is equal in strength and opposite in direction

Action-reaction forces Newton’s 3 rd law is about action-reaction forces It deals with 2 forces. Why do these forces not cancel each other out?

m a =F= m a While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus?

Name that Law! 1)When you put a book on a table, gravity pushes the book down and the table pushes the book up 2)A person is pushed forward into their seatbelt when the car stops 3)A larger car takes more force to move 4)A person leaning on a wall and the wall pushes back 5)A brick sits on a table until you push on it