GIG Read the passage and mark your answers on your whiteboard. NOT ON THE PAPER. Questions 32-33. Take out notebooks and tape or mini-stapler.

Newton’s Laws

Notebook Setup for Chapter 5 Add vocabulary and formulae sheets to your notebooks.

Newton’s Laws So far in physics, we have focused on how to observe and describe motion. Now we will begin looking at why objects move the way they do.

Rolling Marbles Use pencils and marbles to complete the rolling marbles activity. Complete all steps on the activity sheet.

The Law of Inertia Vocabulary terms Force - a push or pull on an object Net force - the vector sum of all forces acting on an object Inertia - the tendency of an object to resist any change to its motion

The Law of Inertia Newton’s first law of motion, also called the law of inertia, states: An object at rest remains at rest unless acted upon by a net force; an object in motion with constant velocity continues moving with the same velocity unless acted upon by a net force.

Newton’s Second Law Newton’s second law of motion states that the force needed to accelerate an object is directly related to the object’s mass. This can be stated in two equations. Newton’s second law for a single force: F=ma Force = mass ✕ acceleration Newton’s second law for multiple forces Net force = mass ✕ acceleration

Newton’s Second Law for One Force

Newton’s Second Law for One Force How do we measure force? With a unit called a newton. One newton (N) is a unit of force able to accelerate 1 kg of mass at a rate of 1 m/s2. 1 N = 1kg✕m s2

Newton’s Second Law for One Force A car with a mass of 1800 kg accelerates at 3.8 m/s2. What is the force pushing it?

Newton’s Second Law for One Force A car with a mass of 1800 kg accelerates at 3.8 m/s2. What is the force pushing it? F = ma F = 1800kg(3.8m/s2) = 6800N

Newton’s Second Law for One Force A newton can also be a unit of weight. What is the mass of someone who weighs 984N? Remember, gravity causes acceleration at 9.81m/s2.

Newton’s Second Law for One Force A newton can also be a unit of weight. What is the mass of someone who weighs 984N? Remember, gravity causes acceleration at 9.81m/s2. 984N = m(9.81m/s2) m = 100. kg (about 220 lbs)

Try this on your whiteboard A fully loaded F-22 Raptor has a mass of 38,000kg and can accelerate at 12.5m/s2. What force is needed to accomplish this?

Try this on your whiteboard A fully loaded F-22 Raptor has a mass of 38,000kg and can accelerate at 12.5m/s2. What force is needed to accomplish this? F = ma = 38000kg(12.5m/s2) = 480,000N

Newton’s Second Law for Multiple Forces Objects frequently experience multiple forces (gravity is one). The sum of the forces, or net force, on an object is a vector. The object will accelerate along that vector.

If the Forces Go Beyond +- Vectors

If the Forces Go Beyond +- Vectors We can break forces down into a 2-D plane, with x and y components. Fnetx =max Fnety =may

If the Forces Go Beyond +- Vectors A rocket is being accelerated horizontal to the ground at 14.5 m/s2. Gravity is pulling it down at 9.81m/s2. What are the net x and y forces on the rocket?

If the Forces Go Beyond +- Vectors A 325 kg rocket is being accelerated horizontal to the ground at 14.5 m/s2. Gravity is pulling it down at 9.81m/s2. What are the net x and y forces on the rocket? Fnetx =max = 325kg(14.5m/s2) = 4710N Fnety =may = 325kg(9.81m/s2) = 3190N

Spring Scales Before we take up Newton’s third law, let’s complete our second activity. You will need 2 identical spring scales. Follow the instructions and complete the activity sheet. Mr. Ryan will come around to check for completion in a while.

Newton’s Third Law of Motion Newton’s third law of motion states that: For every action force acting on an object, there is a reaction force acting on a different object. The action and reaction forces are equal in magnitude and opposite in direction. Did you notice equal forces on your spring scales?

A Footnote about the Limits of Newton’s Laws Newton’s laws of motion accurately describe the everyday motions we see with our eyes in the world around us. There are two areas, however, where they do not apply. At the atomic level, particles follow different laws, a field called quantum mechanics. As matter approaches the speed of light, it follows other rules described in the theory of relativity.

Homework 2-D Motion Problems, due Friday.

Closure Answer on your whiteboard: Why does a string tied to a brick and pulled hard break when a string tied to a styrofoam block and pulled hard accelerates the block?