Unit 2: Gravity and Motion Mr. Ross Brown Brooklyn School for Law and Technology

In this unit we will learn: What is inertia and how does it affect me? How force affects speed or motion. How to estimate the size and direction of a force. The importance of Newton’s three laws of motion.

Aim: How does Inertia Affect the Motion of Cosmic Bodies? Date: 1 April 2016 Do now: If you’re a passenger in a car, what happens to you when the driver slams on the brakes? Why do you wear a seat belt? What happens to a bag of groceries on the back seat?

Aim: How does Inertia Affect the Motion of Cosmic Bodies? Inertia: the tendency of a body at rest to stay at rest, or a body in motion to keep moving in a straight line at a constant speed. Galileo’s experiment Newton’s first law of motion: a body continues in a state of rest or motion in a straight line at a constant speed unless made to change that state by forces acting on it.

Newton’s First Law of Motion A body continues in a state of rest or motion in a straight line at a constant speed unless made to change that state by forces acting on it. Often referred to as the: Law of Inertia

Homework, 8 October 2015 What does Newton’s First Law of Motion tell you about the difference between motion in a straight line and motion along a curve? Be prepared to discuss in class tomorrow.

Aim: How does Newton’s first law explain orbital motion? Date: 4 April 2016 Do now: Think about the amusement park ride where you’re pressed back against the wall of a cylinder and can’t move. Explain the forces at work.

Aim: How does Newton’s first law explain Orbital Motion? Newton’s Cannon Why does the cannonball not continue in a straight line? The balance between inertia and gravity maintains the orbit. With no force – straight line With force (gravity) – curved line Inertia keeps it in motion

Aim: How do acceleration and mass affect motion? Date: 5 April 2016 Do now: If you’re walking down the hall in a straight line, minding your own business, how do other students interfere with your motion? In what ways do they bother you when you simply want to get to class?

How do forces act on objects in motion? Motion: a change in the position of an object Inertia: uniform motion (constant speed and direction) Acceleration: any change in speed or direction Uniform motion: Same speed and direction Acceleration: A change in speed (faster or slower) Acceleration: A change in direction

How does a force affect an object’s acceleration? Acceleration is proportional to force applied, i.e., larger forces produce larger accelerations.

How does an object’s mass affect its response to a force? Mass: a measure of an object’s inertia For the same force an object’s acceleration decreases as its mass increases Which will coast better?

How does an object’s mass affect its response to a force? When a Force, F, acts on an object whose mass is m, it produces an acceleration, a. F=ma Therefore, a=F/m

Newton’s Second Law of Motion The acceleration of a body is proportional to the net force exerted on it, but inversely proportional to the mass of the body.

Homework #6 5 April 2016 Use Newton’s Second Law of Motion to explain why smaller cars get better gas mileage than larger ones.

Aim: What happens when bodies exert forces on each other? 6 April 2016 Do now: How does a rocket lift off and then fly through space?

What happens when bodies exert forces on each other? Newton’s Third Law of Motion Also called the Law of Action-Reaction When two objects interact, they create equal and opposite forces on each other.

Newton’s Third Law of Motion

How do we calculate gravity? 7 April 2016 Do now: What information (data) would you need in order to calculate the force of gravity between two objects?

How do we calculate gravity? The Law of Gravity Every mass exerts a force of attraction on every other mass. The strength of the force is directly proportional to the product of the masses divided by the square of their separation.

How do we calculate gravity? d d2d2

Why else do we care about gravity? Surface gravity: the rate at which all objects accelerate downward similarly. This is the gravitational attraction of a planet’s or star’s surface. Determines weight. Your weight on the Earth is roughly 6 times your weight on the moon because the Earth’s mass is so much greater.

How do we get past earth’s orbit on a rocket? Escape velocity: the speed an object must have to be able to move away from a body and not be drawn back by its gravity.

Homework #6, part 2 7 April 2016 If you weigh 110 pounds on the earth, do you weigh 110 pounds on the moon? Why or why not?