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Force, Mass and Motion S8P3 Students will investigate the relationship between force, mass and motion. Determine the relationship between velocity and acceleration. Determine the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction. Demonstrate the effect of simple machines on work.

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Vocabulary Acceleration – the rate at which velocity changes. (speed or direction changes = acceleration) Acceleration = Example – Turn left onto another road or going down a hill in a car. Negative Acceleration – acceleration in which velocity decreases Example – when a car slows down Deceleration - acceleration in which velocity decreases Example – when a plane slows down to land Final velocity – starting velocity = m/s/s Time

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**Vocabulary Speed – rate at which an object moves (distance/time) (m/s)**

Example – how fast a ball is thrown, car drives Velocity – the speed of an object in a particular direction. (distance/time, direction) Example – The car is driving 5 miles/hour north. Final Velocity – final point at which velocity is measured Example – when a car stops or passes an ending point. Initial Velocity – beginning point at which velocity is measured. Example – When a car starts or passes a beginning point.

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Vocabulary Force – a push or pull. It has size and direction. (Newton (N)) Example – pull open a door, pushing a car door shut. Mass – the amount of matter in an object. (grams (g)) Example – ping pong ball verses a marble Motion – when an object changes position over time when compared with a reference point. Example – running

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Vocabulary Friction – a force that opposes motion between two surfaces that are touching. Rubbing hands together, pushing a box on concrete Inertia – tendency of all objects to resist any change in motion. Example – ball will stay in motion unless another force acts upon it like gravity. Gravity – a force of attraction between objects that is due their masses. Example – ball falls to the ground. Distance – the amount of space between two points. Example – my house is 2 miles from your house

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Speed How Fast???? Have to know Distance an object moves and Time needed to travel that distance Formula Average Speed = Distance Traveled meters/second Time Traveled

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More about speed Most objects CONSTANTLY change speed, so when you use the formula, it is the average speed. If you drive to school, how often do you go 50 mph the entire way? Never.

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**Velocity Speed of an object in a certain direction**

2 cars were traveling at 50 km/sec on the highway for 2 hours. After 2 hours, one car was in Alabama and one car was in Florida. HOW??? Opposite Directions! This is why know the direction is important when calculating velocity.

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**More on Velocity It changes when speed OR direction changes**

You go from 20 mph to 50 mph, you change velocity You go from 20 mph to 20 mph, but turn left you changed velocity. 50 mph North shows velocity Why?

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Acceleration The rate at which velocity changes, so… speed or direction have to change for the acceleration to change. Deceleration: slow down Change in speed or direction = (Final V – Initial V / Time) Another word for Initial velocity is starting or original.

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**Examine the table below for the acceleration of a car**

Examine the table below for the acceleration of a car. You can see the acceleration of the car at any time is 5 m/s/s, so every second, the velocity of the car increases by 5 m/s. Time (second) Velocity (meters per second) 1 5 2 10 3 15 4 20

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**TOTD Give one example of a change in acceleration**

What info do you need to calculate velocity? (3 things) What is the average speed of an object that travels over 100 meters in 20 seconds?

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Inertia Objects resist change in motion. If I am standing still, I will stay that way until…. This is called INERTIA Inertia is wearing a seat belt Example: a car is going 50 mph and comes to a sudden stop, you continue moving a 50 mph, unless something stops you… a seat belt or the dashboard.

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Mass VS Inertia An object with a large mass has more interia. Changing the motion of an object with a large mass is harder than changing the motion of a smaller object. Which would you rather change the motion of? Moving Car or Rolling Soccer Ball

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**Think about it??? Which would you rather stop falling with your head?**

Ping pong ball or marble Which would you rather pull? Tractor or wagon Which would you rather swing? Golf club or grand father clock pendulum?

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**Friction Affects the motion of an object A force that opposes motion**

Friction reduces the speed of an object and releases heat. The amount of friction depends on: Texture of the surface Weight of the object being pushed or pulled The amount of force.

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**Gravity Affects the motion of an object Force of attraction**

The earth is so large that ALL objects are attracted to it Gravity depends on Mass Distance

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**Balanced VS Unbalanced forces**

net force = 0 No motion Total amount of force on an object Unbalanced forces – net force is greater than (>) 0 Motion Object acted on shows movement in one direction.

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**Are these activities balanced or unbalanced forces?**

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FORCE A push or pull Result in motion

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**Mass The amount of matter in an object. NOT Weight of an object**

Your mass is the same whether on Mars, Earth or the Moon. Your weight will change. Ping Pong Ball vs. Marble Feather vs. cotton ball Stick vs bamboo

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Motion A change in the position of an object with respect to time.

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Simple Machines Lever Inclined Plane Wheel and Axle Wedge Pulley Screw

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Work The application of a force to an object to move it a certain distance in the direction of the force. Work = force X distance W = F X D Work is measured in joules (j)

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**Work you do on a machine is input work**

Input Vs. Output Work you do on a machine is input work You apply a force to the machine and move it through a distance Work done by the machine is work output.

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**How do Simple Machines make Work Easier?**

It is a device that makes work easier by changing the size or direction of a force.

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**Inclined Plane Definition How is work made easier Examples (3)**

A straight, slanted surface It is easier to push an object up a ramp than it is to lift the object straight up. Loading a moving truck, slide, wheel chair ramp

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**Wedge Definition How is work made easier Examples (3)**

An inclined plane that is wider or thicker at one end than the other. When moved a wedge is used to cut, split, or pry apart objects Door wedge to hold open a door, scissors, axe, knife blade

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**Screw Definition How is work made easier Examples (3)**

An inclined plane that is wrapped around a cylinder Force is applied over a long distance. Longer the threads the more work. Screw, Spiral staircase, top on a bottle

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**lever Definition How is work made easier Examples (3)**

Made up of a bar that pivots at a fixed point called a fulcrum Based on location of fulcrum and load the work is easier. They apply force to a load. hammer, see-saw, wheelbarrow,

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**Pulley Definition How is work made easier Examples (3)**

Rope or chain wrapped around a wheel Changes the direction of the effort force and/or multiplying effort. Crane, bike, flag pole and flag, climbing gear

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**Wheel and Axle Definition How is work made easier Examples (3)**

Consists of two circular objects of different sizes. Gets more force from the effort compared to the distance. Wheelbarrow, doorknob, bike wheel

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