DEPARTAMEN OF TECHNOLOGY.

074127GT196070210

Levers

ENRIQUE HEREDIA FERNÁNDEZ

LEVERS

Key Questions:

1 Analyze and label the parts of a lever and evaluate how a lever multiplies force.

2 Provide examples of first, second and third class levers.

3 Compare parts of the human body to the types of levers.

4 Calculate and determine the mechanical advantage of a lever.

Forces in Machines

A simple machine is an unpowered mechanical device, such as a lever.

Pulleys

Introducing… The Lever A lever includes a stiff structure (the

lever) that rotates around a fixed point called the fulcrum.

fulcrum

Anatomy of the lever Fulcrum – point around which the lever

rotates Input Force – Force exerted ON the lever Output Force – Force exerted BY the

lever

Levers and the human body Your body contains

muscles attached to bones in ways that act as levers.

Here the biceps muscle attached in front of the elbow opposes the muscles in the forearm. Can you think of other

muscle levers in your body?

Three Classes of Levers First Class - fulcrum

between Input and output

Second Class – output between fulcrum and input

Third Class – input between fulcrum and output

Lever – First Class

Here we have a first class lever The fulcrum is between the input and output Can you get two weights to balance?

Levers in Equilibriu

m

Hang your weights like shown here Does the lever balance? What variables can be changed to balance a lever?

3 2 1 0 1 2 3

Four Variables in a Lever Amount of Input Force F Amount of Output Force R Length of Input Arm L1

Length of Output Arm L2

Lever Challenge Hang weights

from the lever and get it to balance.

Use at least 3 strings!

Do 4 trials and record how many weights to hang and where you hang them.

Lever Challenge

Lever Modification Hang 1 weight

10 cm from the fulcrum.

Where does the output force need to be to oppose our input force?

1 1

Basic Lever Investigation If we move the

input force 10 cm, how much more do we need to add for the same output force?

Try it...

1

Basic Lever Investigation If we move the

input force 10 more cm, how much more do we need to add for the same output force?

Add two masses at 20 cm.

HINT: you will need two strings

1

Mathematical Rule for Balancing the Lever

What mathematical relationship can you find that will balance the lever every time?

Put your rule in terms of input and output and forces and distances.

What if there is more than one location on either side of the lever?

What is the Relationship?

Force x Distance = Force x Distance

Input Force x Length of Input Arm

# of Weights x Distance

Output Force x Length of Output Arm=

# of Weights x Distance=

What if there several groups of weights ?

Sum of Input = Sum of Output

(F1 x D1) + (F2 x D2) (F3 x D3) + (F4 x D4) =

T

END