Chapter 12 – Forces & Motion

Forces Force – a push or a pull that one body exerts on another body. * these boys are pulling on the rope and therefore are applying a force to it.

Forces Force – a push or a pull that one body exerts on another body. * this boy is pushing the ball with his foot and therefore is applying a force to it.

Forces Force – a push or a pull that one body exerts on another body. In the English system forces are measured in units called pounds. In the Metric system forces are measured in units called Newtons. (This is what we will use in class) 1 pound = Newtons (so if you weigh 100 pounds that would equal Newtons

Forces Force – a push or a pull that one body exerts on another body. We can use Vectors (arrows) to show direction of force and how big the force is (see below) *these arrows are different directions and different sized forces. Which team should win?

Forces 2 Categories of Forces Balanced Forces - forces that are equal in size, but opposite in direction (shown below) - In the case of the tug-of-war no one would move if they are pulling with the same force but in opposite directions ** The result of balanced forces is no change in motion!!!

Forces 2 Categories of Forces Unbalanced Forces - forces that are not equal in size,(shown below) - In the case of the tug-of-war the team applying the larger force will accelerate in that direction. ** The result of unbalanced forces is a change in motion!!! ACCELERATION

Forces Types of Forces Friction- Forces that oppose motion of objects that touch as they move across each other 4 types of friction Static Friction – friction force that acts on objects that are not moving Even though the desk is tipped the calculator doesn’t move because the frictional force is enough force to oppose motion

Forces Types of Forces Friction- Forces that oppose motion of objects that touch as they move across each other 4 types of friction Sliding Friction – friction force that opposes motion of an object as it slides over a surface As the tree slides across the ground the friction between the tree and the ground makes it harder to move

Forces Types of Forces Friction- Forces that oppose motion of objects that touch as they move across each other 4 types of friction Rolling Friction – friction force that acts on rolling objects As the ball rolls down the lane there is friction between the floor and the ball

Forces Types of Forces Friction- Forces that oppose motion of objects that touch as they move across each other 4 types of friction Fluid Friction – friction force that acts on objects that are moving through a fluid As swimmer moves through the water there is friction between their body and the air and water (both fluids)

Go to Moodle and watch Jeans & Friction & Friction Video **You must have ear buds to watch these videos Click button to watch

Forces Types of Forces Gravity – force of attraction between two objects that have mass The amount depends on 2 things: Mass – the larger the mass the larger the gravitational force moon Earth *The earth is about 1/4 th the size of the Earth and therefore has a smaller gravitational force

Forces Types of Forces Gravity – force of attraction between two objects that have mass The amount depends on 2 things: Distance apart – the farther apart two objects are from each other the weaker the gravitational force and the closer they are the stronger the gravitational force. The closer a satellite is to Earth the stronger the gravitational force between the Earth and the satellite.

Forces Types of Forces Gravity – force of attraction between two objects that have mass ** Causes objects to fall – and when they fall they ACCELERATE **The longer things fall the faster they go!

Forces Types of Forces Gravity – force of attraction between two objects that have mass ** when they fall they ACCELERATE (go faster) - As a penny falls off a building it starts out falling slowly, but the longer it falls the faster it goes. * Until it reaches TERMINAL VELOCITY

Forces Types of Forces Terminal velocity – the maximum speed reached by a falling object Reached when upward force of air resistance = downward pull of gravity (weight) 5 N 10 N Weight Air - The leaf is still accelerating because the downward force is greater than the upward force

Forces Types of Forces Terminal velocity – the maximum speed reached by a falling object Reached when upward force of air resistance = downward pull of gravity (weight) 10 N Weight Air - The leaf is NOT accelerating because the downward force is equal to the upward force

Forces Types of Forces Terminal velocity – the maximum speed reached by a falling object Reached when upward force of air resistance = downward pull of gravity (weight) 5 N 10 N Weight Air Still accelerating Stopped accelerating

Projectile Motion Projectile – anything shot or thrown through the air * Must have forward motion and downward motion and the path is always curved If there was no gravity the ball would travel straight forward

Projectile Motion Projectile – anything shot or thrown through the air * Must have forward motion and downward motion and the path is always curved If there was no forward push the ball would travel straight down

Projectile Motion Projectile – anything shot or thrown through the air * Must have forward motion and downward motion and the path is always curved Because there is gravity and a forward push the result is a curved path – a combination of the two