Forces and Motion
A force is
a push or pull.
- You push on a door
- The force of the wind pushes
sailboats and windmills
The amount
of force you have to use to move an object depends on its mass.
- I bring a cardboard box
(originally for apples) and a rope into the classroom. I chose a tall
learner and a short learner. First the short learner sits down in the box
and someone pushes him or her through the room. Then I tell the tall one
to sit in the box. The learners laugh. They know, that it is much harder
to push that one!
Motion is a
change in position. Every motion is started and ended by a force.
- If we throw (pushing force) a
ball and nobody is there to catch it, in theory, it could fly on forever,
but gravity pulls it down and makes it stop on the ground.
Gravity is
the force that causes all things to fall to the ground.
Simple Machines
A simple
machine is a tool that helps people to do work.
There are
six types of simple machines:
Lever
Pulley
Wheel and
axle
Inclined
plane
Wedge
Screw
I show the
learners a lot of pictures and let them identify the type of simple machine.
Inclined plane
An inclined
plane is a flat surface set at an ancle to another surface/the ground.
Example: A
load is pushed along the inclined plane onto a truck.
We build an
inclined plane using our rulers as an inclined plane and our rubbers/sharpeners
as heavy load.
Screw
A screw is
like an inclined plane wrapped around a pencil.
Example:
Screw, bottletop
Lever
A lever is
a bar that moves on or around a fixed point (called the fulcrum).
I
demonstrate the fixed point to my learners with a red drawing-pin.
Examples:
- Arm
- Seesaw
- Balance scale
- Pair of tongs, pliers
- Pair of scissors
- Bottleopener
- Crowbar
- Wheelbarrow
- Hammer
We build a
seesaw ourselves using a ruler, a pencil and a small object as a load. The
pencil is the fixed point/fulcrum of the seesaw. The ruler is the bar. As small
object you can use a rubber.
Wedge
A wedge is
two inclined planes stuck back to back.
Example: An
ax. A pair of scissors is made up of two wedges.
Wheel and axle
In a wheel
and axle, the wheel is larger than the axle. It takes less force to move the
wheel than to move the axle. But when the wheel makes a circle it goes a longer
distance than the axle.
Example:
Bycicle.
Pulley
A pulley is
a rope over a wheel.
It changes the direction of the force that you use. When
you pull down one end of the rope, the bucket at the other end moves up.
Because of gravity, pulling down is much easier than pulling up. Pulling down
there are two forces: you and gravity. Pulling up you have to fight gravity.
We build a
pulley.
Materials needed: empty toilet tissue rolls, wool, a small object as
`load´, a pencil.
Put the pencil through the paper roll. The pencil is the axle
and the paper roll the wheel. Wind the wool two times around the roll and
attach a load like a pencil sharpener to one end of the wool. Then pull down
the other side of the wool and see how the load is moved up!
Simple Machines poem
It´s easy
to find – a plane that is inclined!
The edge
looks like a – wedge!
Ouch, in my
shoe there is a – screw! Screw you!
I hurry to
pull the – pulley!
I think
it´s clever to use a – lever!
For an easy
deal I use – axle and wheel!
