REMEMBER
Both pulley systems need the same amount of
“work” to pull the basket up to the t
op. With the
fixed pulley you need the full amount of ener
gy,
but only one length of rope. If you us
e the fixed
pulley and the movable pulley together
, you only
need half as much effort, but you hav
e to pull
twice as far (two lengths of rope).
Attach your hoist to the treehouse and transport small “loads” up to the top. Don’t ever hang more
than 500 g (the weight of two sticks of butter) on your hoist!
?
WHAT’S HAPPENING
Your basket is now hanging on two strings.
The “movable pulley“ moves upward when
you pull on the end of the string. Did you
notice that it’s also easier to pull the
basket up to the top? In fact you need
exactly half as much “effort” (or “force”).
By using one fixed and one movable
pulley, this “block-and-tackle” hoist has
changed three things:
1) You’re pulling downward instead of
upward.
2) You only need to use half as much
effort to pull the basket up to the
top.
3) But you need twice as much
string — double the length — to
transport Pepper up to the top.
… Hang the basket onto the lower hook, the
one you knotted the string onto. Put your
Pepper Mint figure, or a pile of coins, into the
basket and try pulling it up to the top.
4
Now you’re going to add a “movable pulley”.
Swap the two hooks around: Now the hook with
the loose string is carrying the basket. Attach
the other hook, the one that’s knotted onto the
end of the string, to the top of the treehouse.
5
Thread the loose end of the string up and
over the pulley attached to the hook that’s
fixed at the top, then down again. Put Pepper
in the basket and pull her up to the top.
4
5
14
and the
Hoist
