Cranes
How do cranes on building sites work?
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  Facts
  • A crane is a tall machine that uses engines to lift heavy objects
  • A crane has a tall mast (like the mast on a sailboat) and a long arm called a jib (like the front sail on a sailboat).
  • The trolley on the arm is the part of the crane that works to pick up things.
  • It lowers and raises a hook or a bucket on the end of a strong metal rope called a cable. The trolley can also move from the end of the jib all the way back to the mast.
  • The crane driver sits in the cab at the top of the mast where they get the best view of what’s going on.
 
  Did You Know?
  • A crane needs to be taller than the highest point it will need to lift objects to.
  • It needs to have a firm foundation and a crane can often have foundations set deep into the ground.
  • It also needs a counterweight at the back of the crane so it doesn’t overbalance.
  • A crane is made up of lots of triangle shapes which is the strongest shape you can get because no matter how you pull or push it a triangle will hold its shape.
 
  Experiments
Do the shape test

What you need:
At least 4 cardboard rolls from lunch paper or plastic food wrap
At least 4 clean ice block sticks.
A pair of scissors
A large lump of plastercine/play dough or a Ball of scrunched up paper
The help of a friend

What you do:
Stuff the scrunched up paper or the lump of play dough into one end of a cardboard roll. Carefully use the point of the scissors to push a hole through the cardboard into the paper or play dough. Do the same on the other side of the roll and then on both ends of the other rolls.
Push an ice block stick through the holes in the ends of two rolls to join them together. Do the same with the other ends of the two rolls to make a square shape. You may need to use the plastercine/play dough to hold the sticks in place. Gently try moving the square by pushing on one or two of the sides. Can you push it out of shape?
Try making a triangle out of the rolls. Push the triangle out of shape. Can you change the shape without damaging the rolls?
 
  Investigation
Next time you’re near a building site watch a crane in action. You don’t have to get close – in fact you can often have the best view from further away. Watch the jib (or arm) turn around and the trolley move along the jib. See if you can see all the triangle shapes used to make the crane strong.
 







 
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