What You Already Know
Technology is using science to solve problems. Technology
changes over time. Technology helps people. Tools and machines are kinds of technology.
They help people do work. Tools and machines are used to farm. They are used to
build. Tools and machinesare also used to communicate.
Simple machines are tools that have few or no moving parts.
People use them to do different kinds of work. Wedges push things apart. Wheels
and axles move things. Screws hold things together. Levers lift things. Pulleys
and inclined planes move things up and down. Simple machines help people work.
Some big machines are made up of simple machines. The big machines in this book
help people build things.
On Site
Have you heard the roar of busy machines at a
building site? Have you ever seen the different machines at work? Many
different machines are used to build buildings on a site. You might see
machines that dig. You might see machines that pick up and drop or dump.
Bulldozers, wheel loaders, and cranes can all help on a building site.
Each big machine has a job to do. Some machines
carry. Some machines push. Some machines lift. But they are all alike in an
important way. They help people do hard jobs! These big machines are alike in
another way too. They have simple machines in them. Some of these big machines
use wheels and axles, screws, levers, and pulleys to do their work.
Diggers
Just say the name and you will know what diggers do.
They dig! They dig big holes. The long arm of the machine bends down to the
ground. The bucket digs into the ground. Then it scoops up a load of rocks,
sand, and dirt.
The arm lifts the bucket up when it is full. The
digger swings around and dumps the load. Then the digger turns back to the
hole. It is ready to lift another load!
Dump Trucks
Dump trucks move heavy loads. They carry the loads
across building sites. Some dump trucks move loads away from the building site.
Other dump trucks bring loads to the building site. Dump trucks can move lots
of sand and dirt in and out of the site!
Pedals and levers lift the dump truck’s box. The
arms push the box up. The back of the dump truck swings open to unload. The
load rumbles and tumbles out of the box. It falls onto the ground. Then the
driver brings the empty box back down.
Bulldozers
A bulldozer’s job is to make the ground flat. The
big blades push heavy loads of stones and dirt over the ground. Other big
machines can go to work after a bulldozer has made a place flat and clear. Bulldozers
do not have tires. They move along on tracks.
The tracks are made of many little parts that join
together. They spin around to move the machine. The tracks grip the ground.
They keep the big machine from sinking into mud. A bulldozer is a slow-moving
machine. But do not let that fool you! It is one of the most powerful machines.
It can push very heavy loads!
Wheel Loaders
And Forklifts
Wheel loaders and forklifts move big loads from one
place to another. These machines can have different parts on the front. The
different parts help move different things. Some have scoops on the front. Some
have forks.
All wheel loaders have a moving arm. Levers slide
the forks or the scoop under the load. Levers lift the load up off the ground.
Then the machine moves the load to a new place.
Cranes
Cranes are tall machines that lift and move heavy loads.
Cranes use pulleys to move their loads. Different kinds of cranes do different
jobs. Some cranes load things on ships. Some cranes lift things to the tops of
tall buildings. Some cranes even lift other cranes!
Keep your eyes open the next time you pass a
building site. Maybe you will see diggers, dump trucks, bulldozers, wheel
loaders, and cranes at work. Each one uses simple machines to get the heavy
jobs done!
Glossary
bulldozer a heavy machine used to clear
crane a tall machine with a long arm that lifts, moves, and lowers
digger a machine used to make holes in the ground
dump truck a machine that carries, moves, and unloads
load something that is carried site a place
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