Page 21 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

2 Making Things Move

echanical systems come in many shapes and forms, and they have various
Mdefinitions. Before we can start making machines, we need to know what
we’re talking about:

• A mechanism is an assembly of moving parts.
• A machine is any device that helps you do work, from a hammer to a bicycle.
A hammer is a machine because it makes your arm longer, so you can do
more work.

In this book, we use the mechanical definition of work:

Work = Force × Distance

Force (F) equals mass (m) times acceleration (a), and is written as F = ma (also known
as Newton’s second law).
For example, imagine that you’re stomping on a bunch of grapes to make wine. The
force the grapes feel when you stand still is equal to your weight, but the force the
grapes feel when you stomp is your weight plus the acceleration your muscles give to
your foot. The grapes would feel less force, however, if you were stomping them on
the moon, which has just one-sixth of the Earth’s gravity. Mass refers to the amount
of stuff you’re made of, which doesn’t change. Gravity and acceleration depend on
where you are and what you’re doing. So, mass is the stuff, and weight is the force
that the mass exerts.

Six Simple Machines

The four main uses of machines are to:

1. Transform energy A windmill transforms energy from the wind into
mechanical energy to crush grain or electrical energy to power our homes.

2. Transfer energy The two gears in a can opener transfer energy from your
hand to the edge of the can.