Force, Mass and MotionS8P3 Students will investigate the relationship

between force, mass and motion.

a.Determine the relationship between velocity and acceleration.

b.Determine the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction.

c.Demonstrate the effect of simple machines on work.

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 velocityTime

= m/s/s

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.

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

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

Speed

How Fast???? Have to know Distance an object moves

and Time needed to travel that distance

Formula • Average Speed = Distance Traveled

Time Traveled meters/second

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.

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.

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?

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.

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)

0 0

1 5

2 10

3 15

4 20

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?

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.

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

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?

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.

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

Balanced VS Unbalanced forces

Balanced 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.

Are these activities balanced or unbalanced forces?

FORCE

A push or pull Result in motion

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

Motion

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

Simple Machines

Lever Inclined Plane Wheel and Axle Wedge Pulley Screw

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)

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.

How do Simple Machines make Work Easier?

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

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

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

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

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,

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

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