Force & Motion; Earth’s History NOtes Shartzer – 8th Grade Force & Motion; Earth’s History NOtes

Newton’s Laws of Motion SC-08-1.2.1 – Students will describe and explain the effects of balanced and unbalanced forces on motion as found in real-life phenomena. It all began …

Speed versus Velocity D S T v Speed Velocity Definition How fast or slow an object is moving Calculate speed by: distance divided by time Metric Units for Speed meters per second (m/s) Examples of speed 55 m/s 15m/s How fast or slow an object is moving plus the direction an object is traveling Calculate velocity by: -------------distance divided by time and add direction to your calculation Metric Units for Velocity Examples of velocity 55 m/s west 15 m/s downhill D D S T v T

So, How do things Move? Moving – an object is moving if it changes position and the background is stationary. Speed – describes how fast an object moves. Calculate speed – Distance divided by Time speed=distance/time Constant Speed – when an object covers equal distances in equal amounts of time. There is no speeding up or slowing down. Average Speed - Total distance divided by total time

How Do I Graph the Motion of a Particle? NSF North Mississippi GK-8

What are some examples of objects that move at high velocities? NSF North Mississippi GK-8

What are some examples of objects that move at low velocities? NSF North Mississippi GK-8

What units would you use to measure the velocity of an object moving in this classroom? meters per second Meters per second tells us how many meters something can move in one second. NSF North Mississippi GK-8

What else can we know about an object’s motion besides velocity? What if the object speeds up? What if the object slows down? What if the object’s velocity changes? NSF North Mississippi GK-8

Scientists have a special way to measure a change in velocity: Acceleration Acceleration is a change in velocity. NSF North Mississippi GK-8

The Way Acceleration Works: If you’re speeding up, you have positive acceleration. If you’re slowing down, you have negative acceleration. If you’re changing speed quickly, you have high acceleration. If you’re changing speed slowly, you have low acceleration. NSF North Mississippi GK-8

Example: You’re driving along in your car and suddenly have to slam on your brakes for a red light. Negative or positive acceleration? High or low acceleration? High negative acceleration because you’re slowing down quickly. NSF North Mississippi GK-8

Example: You’re an astronaut waiting in your shuttle for takeoff. Suddenly the rockets fire and you’re on your way to Mars. High or low positive or negative acceleration? High positive acceleration because you’re speeding up quickly. NSF North Mississippi GK-8

Example: You’re driving down the highway when your car runs out of gas and you slowly roll to a stop on the side of the road. Low negative acceleration because you’re slowing down slowly. NSF North Mississippi GK-8

Example: You’re walking to class when you realize you’re running just a little bit late. You start walking a bit fast, but you still hope to make it on time. Finally the bell rings so you break into a jog and then a run, trying to get to class before the teacher notices you’re late. Low positive acceleration because you’re speeding up slowly. NSF North Mississippi GK-8

Challenge Question: You throw a baseball straight up in the air. It rises to a certain height and then falls back to earth, where you catch it again in your glove. First, high positive acceleration because it speeds up quickly as it leaves your hand. Then, as it rises, low negative acceleration, because it begins to slow down slowly because of gravity. As it begins to fall again, low positive acceleration, because it speeds up slowly. Finally, when you catch it, high negative acceleration because it slows down very quickly in your hand. NSF North Mississippi GK-8

Acceleration and Force Definition Any change in velocity Calculating Acceleration Acceleration = Ending Velocity – Starting velocity Time

The product of an object’s mass and velocity Momentum Momentum Definition The product of an object’s mass and velocity Calculating Momentum Momentum (P) = mass * velocity Units of Momentum Kg*m/s Example A bowling ball has momentum when it hits the pins because the ball has mass and velocity. P M V

Balanced Forces Equal forces acting on one object in opposite directions

Unbalanced Forces

Unbalanced Forces

Net Force in the same direction

Net Force in opposite directions

A Force that occurs when two objects oppose or rub against each other. Friction A Force that occurs when two objects oppose or rub against each other.

Types of Friction Sliding friction: when solid surfaces slide over each other Rolling friction: when an object rolls over a surface Fluid friction: when an object moves through a liquid or a gas Static friction: prevents an object from moving when a force is applied

Newton’s First Law of Motion An object at rest will remain at rest, an object that is moving at a constant velocity will continue to move at a constant velocity unless acted upon by an unbalanced force. Also called the “Law of Inertia”.

Newton’s Second Law of Motion The net force on an object is equal to the product of its acceleration and its mass.

Different ways to show Newton’s 2nd Law M A