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Discuss how machines make work easier. Identify machines such as a bus, a stapler, or a bike. While machines can have many moving parts, a simple machine has none or very few moving parts. A simple machine can change the direction or significance of a force in different ways to make work easier. It can change the way a force is used to make it more effective. A ramp, or inclined plane, is a simple machine with a slanted surface. It helps people and things move between higher and lower places. Discuss different ramps children have seen or used, such as moving ramps, disabled accessibility ramps, or slides on the playground. Explain that it takes a lot of force to lift and move something heavy, but it’s much easier to push it up a ramp. It is much harder to move things up steeper ramps, or ramps that go up higher, just as it is harder for people to walk up a bigger or steeper hill. A lever is a simple machine that consists of a bar that rests on a fulcrum, or a point that does not move. A lever can also help lift up heavy loads. A seesaw is the classic example of a lever. When force is applied to one side and is pushed down, the other side lifts up. Any tool that pries something loose is a lever, like the claw side of a hammer or a bottle opener. Scissors and staplers are common items that use levers. A wheel and axle work together to make a simple machine. Explain that a wheel turns around a rod, called an axle. A wheel and axle can help move things faster or more easily, and also help things turn. Carts, skateboards, roller skates, bikes, and cars all use wheels and axles. Explain that heavy things can be difficult to push across a surface and can require a lot of force. But, if you add wheels to the bottom, it becomes much easier. Wheels and axles can act as fulcrums, as well. A wheelbarrow can lift and carry very heavy items using wheels as rotating fulcrum points. Have children give examples of how wheels and axles make work easier. A pulley is a simple machine that has a rope or cable that goes over a wheel. A pulley helps people lift things up and change the direction of their force. You pull on a rope to make the load go up. You can also connect pulleys together, creating a combined pulley that requires less than half the force otherwise needed to lift up a load. Clotheslines, flagpoles, and blinds use pulleys. Help children understand that combining simple machines can also make work easier. Any two or more simple machines put together are known as compound machines. Many machines are compound machines. For example, a crane uses levers, wheels and axles, and many pulleys to lift up heavy objects. Learning about simple machines and forces is a great way to teach the fundamentals of physics and help children understand the world around them.
Materials: spring scales, marbles or pennies, bags (fabric or Ziploc baggies), rulers, pulleys with cord, (foam core board, binders, or train tracks for ramps), lab handout Conclusion How did the work without a machine compare to the work done with a machine? (THEY SHOULD BE THE SAME) How did the force needed to lift the object without a machine compare to the force needed with a machine?
Effort force acts on double the distance the load is raised = MA of 2 Effort force if half the weight of the load = MA of 2
Overview only - next slide has more detailed explanation.
First class levers: pop can, screw driver on lid, seesaw, catapult, pump handle Second Class: wheelbarrow, bottle cap, nut cracker Third Class: fishing pole, snow shovel, ice tongs/tweezers, chopsticks
Work & Simple Machines
Work &Work &
Work: the transfer of energy that occurs
when a force moves an object.
a force must act on the object the entire distance
the object must move in the same
direction that the force is applied
Pulling up on the bar while the
weight is on the ground (no
movement) is NOT work.
Holding the barbell overhead
is NOT work.
Lifting the weight up IS work.
If 10 N of force is applied to this cart,
moving it 20 m, how much work is done?
W = F x d
W = 10 N 20 m
W = 200 Nm
1 Joule = 1 N force that
moves an object 1 m
W = 200 J
Mechanical energy =
The ability to do work
The amount of work done
Has same units as work (Joules)
Intro to Machines
A machine is a device that makes work easier.
Work & Machines
A machine makes work easier by changing the
direction or size of the force needed to move
an object. (They cannot save or reduce work)
W = Force x distance
All machines are made up of one or more of these 6
Each one reduces the amount of force needed to
M.A. = resistance force
A machine allows you to lift an 8N block with 4N of force
Mechanical Advantage = 8N/4N = 2
M.A. of 2 means your effort force is doubled
Change of direction:
A machine lets you lift a 10 N block with 10 N of force
Mechanical Advantage = 10N/10N = 1
M.A. of 1 means the direction of your effort force is changed
How is work done? Measured?
Work is force applied through a distance.
The direction of force and motion must be parallel for work to be done.
W = F x d = Energy
How do simple machines make work easier?
Less force over longer distance, or direction of force is changed (amount of work
stays the same)
How will using a lever, pulley, or inclined plane affect the work
of lifting a bag of pennies?
•Fill a bag with pennies (make sure it is within the measurable range of your spring scale).
•Measure the height and length (distance) of your “ramp” and record it in the data table.
•Slowly & steadily pull the bag of pennies to the top of the ramp with a spring scale.
•Watch the spring scale and note the force required to move the pennies up the ramp (in newtons).
•With a spring scale, lift the pennies straight up to the same height as the top of the ramp; record the force.
•Repeat steps 2-5, using other simple machines to lift the same weight the same distance.
Inclined plane: any flat, slanted surface
A ramp is the most common type of inclined plane.
higher at one end than the other
the longer the ramp, the less force is needed to do the work
Inclined planes help by pushing up against gravity's
pull on the load (normal force).
The load (resistance) moves in the same direction as the
Wedge: two inclined planes put together to form
used to lift or pry apart heavy objects
can also stop an object from moving
A wedge works as the two inclined planes push
at perpendicular angles on the load.
The load moves in a different direction
than the effort force.
In this picture, as
the force moves the
ax down, the load
apart and falls to
Screw: an inclined plane
wrapped around a center post
longer inclined planes (more/closer threads) require
less force to move the load
has two parts: the inclined plane and the center post
As the force rotates the screw, it goes down into
The force and the load move in the same direction.
Threads of screw increase surface area friction which allows
screws to objects together better than nails
Wedge-shaped post allows screw to go in wood easier
Lever: a straight bar that moves on a fixed point called
the longer the distance between effort force and the fulcrum, the
less force will be needed to move the load
has two parts: the bar and the fulcrum
A lever works to change the direction of effort force
and/or the distance the force acts throughout.
Load & force move in opposite directions (1st
use gravity's pull on your own weight as the downward force
Moving the fulcrum changes the distance needed to push down
pushing the lever two feet down results in moving the rock up 1 foot
First Class Lever:
Fulcrum in middle, load & force on opposite ends
Load & force move in opposite directions.
Second Class Lever
Load is in middle, with effort on end.
Load & force move in same direction.
Third Class Lever
Bar is attached to fulcrum on one end.
Load is on end, with effort in middle.
Load & force move in same direction.
Wheel & Axle
Wheel and axle: a circular disc locked to a center post.
The larger the wheel, the less force needed to move the load.
two parts: the wheel and the center post (axle)
When the wheel turns, it forces the axle to turn; or if the axle is
turned, the wheel also turns.
One full turn of the large wheel results in one full turn of the smaller
The force moves in the same direction as the load.
Pulley: a grooved wheel with a rope around it.
The larger the wheel, the less force will be needed to
move the load.
two parts: the wheel and the rope
Pulleys can change the direction and/or amount
of force needed to move the load.
Load & force move in opposite or same directions,
depending on how pulley is attached.
As the rope is
pulled down, the
flag goes up.
When used in combination, pulleys
increase the mechanical advantage.
To calculate the M.A., count the # of pulley
ropes pulling on the load
Some tools have two or more simple machines
2 levers joined at fulcrum
blades are wedges
two wheel and axel machines
screws (hold frame together)
levers (pedals and hand brakes)
wheel & axle