Distance Time Graphs Slope movement Positive slope movement

Distance - Time Graphs Slope = movement Positive slope = movement away from starting point Negative slope = movement toward starting point Flat line = no movement (at rest or standing still)

Speed -Time Graphs Slope = acceleration If slope is positive = positive acceleration If slope is negative = negative acceleration If slope is flat = constant speed

Compare Speed-Time Distance-Time

Forces Chapter 12

What is a Force? Force = a push or pull one body exerts on another Can cause acceleration or deceleration Friction & Gravity are 2 main types of force

Balanced Forces = opposing forces balance out Unbalanced Forces = one force is greater than an opposing force and will cause movement

Static Friction Static friction = force that acts on objects that are not moving Ex: When you step forward, your shoe doesn’t slide backwards b/c of static friction

Sliding Friction Sliding = force that opposes an object’s motion as it slides across a surface Ex: Pushing a box across the floor/ground

Rolling Friction Rolling = force that acts against rolling objects Ex: easier to move heavy items w/ wheels or a hand truck

Fluid Friction §Fluid = force that opposes motion of an object through a fluid Ex: stirring brownie mix or swinging a bat through the air

Gravity Force exerted by every object in the universe on every other object Gravity pulls down on the object (toward the center of the Earth) and adds more resistance.

Newton F = ma Force = mass x acceleration SI unit for Force = N (Newton) 1 N = amt of force needed to accelerate a 1 kg object at a rate of 1 meter/second 2 N = kg • m/s 2

According to Newton's first law. . . An object at rest will stay at rest unless acted on by an unbalanced force. An object in motion will stay in motion (with the same speed and in the same direction) unless acted upon by an unbalanced force. This law is often called "the law of inertia". Eventually Friction & Gravity will act on an object & caused them to stop moving (except in space – no gravity, no friction)

What does this mean? This means that there is a natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion.

Let's study the "skater" to understand this a little better. What is the motion in this picture? What is the unbalanced force in this picture? What happened to the skater in this picture?

This is the reason you should always wear your seatbelt.

According to Newton's second law. . . Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

What does this mean? Everyone unconsciously knows the Second Law. Everyone knows that heavier objects require more force to move the same distance as lighter objects.

The Second Law gives us an exact relationship between force, mass, and acceleration. FORCE = MASS times ACCELERATION

An example of how Newton's Second Law works: Mike's car, which weighs 1, 000 kg, is out of gas. Mike is trying to push the car to a gas station, and he accelerates the car at 0. 05 m/s/s. Using Newton's Second Law, you can compute how much force Mike is applying to the car. F=ma F=1000 kg • . 05 m/s/s = 50 kg • m/s/s 1 kg • m/s/s = 1 Newton 50 kg • m/s/s = 50 Newtons

Momentum = mass • velocity p = mv Ex. - Newton’s Cradle

Determine the momentum of a. . . a. 60 -kg halfback moving eastward at 9 m/s. p = m • v = 60 kg • 9 m/s p = 540 kg • m/s, east b. 1000 -kg car moving northward at 20 m/s. p = m • v = 1000 kg • 20 m/s p = 20 000 kg • m/s, north c. 40 -kg freshman moving southward at 2 m/s. p = m • v = 40 kg • 2 m/s p = 80 kg • m/s, south

According to Newton's third law. . . For every action there is an equal and opposite re-action. Ex. = Your desk & You

What does this mean? This means that for every force there is an equal and opposite reaction. When an object pushes another object it gets pushed back in the opposite direction equally hard.

How a rocket works The rocket's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force. UP, and AWAY!

Quiz Time 1. Who was the scientist who gave us the Laws of Motion? Answer: Sir Isaac Newton 2. How many Laws of Motion are there? Answer: three 3. What is another name for the first law of motion? Answer: Law of Inertia 4. Which law explains why we need to wear seat belts? Answer: First Law of Motion 5. Which law says that force is equal to mass times acceleration (F=MA)? Answer: Second Law of Motion 6. Which law says that heavier objects require more force than lighter objects to move or accelerate them? Answer: Second Law of Motion 7. Which law explains how rockets are launched into space? Answer: Third Law of Motion 8. Which law says that for every action there is an equal and opposite reaction? Answer: Third Law of Motion

Newton’s Cradle

Add to your notes Scalar – anything with a value (a number) i. e. – age, cost, speed, etc. Distance can be scalar Vector – anything with a value & direction i. e. – velocity, acceleration, displacement (should be) Distance can be a vector (include direction)

Fg = mg Force (with gravity applied) = mass • gravitational acceleration Fg = weight

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