Unit 2/3 Science Review

(FORCES, MOTION, AND

SIMPLE MACHINES)

Force – any push or pull(includes contact and non-contact forces)

Combined forces – when two or more forces are working at the same time (can include contact and non-contact forces)

Examples:

Friction combined with pedaling a bike

Several people pulling on a rope in tug-of-

war

Gravity combined with a squirrel pushing

an acorn from a tree

Friction – a contact force that goes against motion

When there is more friction, there is lessmotion. Friction slows down the motion of objects.

Friction Motion

Examples of surfaces that create a lot of friction

Rocks/gravel

Carpet

Tall grass

Sandpaper

Concrete

Examples of surfaces without much friction

Smooth ice

Polished floors

Smooth glass

Polished marble and granite

When can friction

be helpful?

Friction can be helpful to prevent slipping or to help us slow down or stop when we need to stop.

Examples:

Brakes on cars and bikes

Sand or salt on an icy driveway

Jagged tips on ice skates

What is gravity?

Gravity is a non-contact force that pulls objects toward each other.

Examples of how gravity works:

It pulls skydivers back towards Earth

It keeps people and objects from floating into space

It keeps the planets in orbit around the sun

Causes objects such as baseballs or apples to fall to the ground

Simple machines

Inclined planes – i.e. ramps

Wedges – i.e. axes and knives

Screws – i.e. spiral slides and drywall

screws

Levers – i.e. seesaws

Wheel & axles – i.e. Ferris wheels, tires

Pulleys – i.e. on flagpoles and sailboats

Simple machines and work

Simple machines do NOT create

less work.

They make it so that less force

can be used to complete the

work.

Tug of war

When the same amount of force is applied from both teams, the rope does not move.

One team can win the game by applying more force to the rope than the other team.

What is work?

Work is when you use force to move an object.

When an object does not move, work has not occurred.

Examples of work:

Hauling rocks

Kicking a soccer ball across a field

Mowing the grass

Moving boxes into a van

Speed

Speed is how fast an

object changes

position.

Constant speed –when objects remain

at the same speed

Variable speed –

when objects change

directions and/or their speed

Figure out a person’s running Speed

If Jan can run 2 miles in 14

minutes, how fast can she

run each mile?

14 ÷ 2 = 7 minutes per mile

Magnetism

A non-contact force that causes

attraction of objects containing certain

metals, such as iron, to magnets.

Position and relative position

An object’s position has changed if it

is in a different location.

Relative position is the position of one

object compared to the position of other objects. For example, the

relative position of a racecar is

important because it is being

compared to the position of other

racecars.

Motion

You can tell an object is in

motion if its position changes.

How could you describe the motion of a Ferris wheel? It

has a circular motion.

If you apply the

same amount of

force to two

objects, which one

will go further?

The one that weighs less will

go further.