Key Questions:

What is torque?

How do we calculate torque?

Performance Objectives

Measure forces and distances in a simple machine.

Calculate torque.

Apply the concept of mechanical advantage to levers.

Build three classes of levers.

Lever Assembly

SAFETY NOTE:

WATCH for FALLING weights on bare toes or sandals or table tops!

DO not place the fulcrum higher than hole 3 of stand!

Torque

Levers use torque to lift or move objects.

Torque is a force applied over a distance that causes ROTATION to occur.

Torque is measured in Newtonmeters (Nm)

Review of levers

Force x Distance = Force x Distance

Input Force

x Length of Input Arm

Torque

Output Force

x Length of Output Arm

=

Force= DistanceX

An Example of Torque

Calculate the torque created when opening the door.

1. Set up the balanced lever

2. Measure Forces and 3. Calculate input/output torques

Calibrate the spring scale

Data

Torque and direction If more than one torque acts on an object, the

torques are combined to determine the net torque.

If the torques tend to make an object spin in the same direction (clockwise or counterclockwise), they are added together.

If the torques tend to make the object spin in opposite directions, the torques are subtracted.

Torques causing counterclockwise rotation are positive and torques causing clockwise rotation are negative.

Forces and Machines

The variables in a simple machine can be adjusted make work easier or resist forces on purpose.

Consider two levers:

Forces and Machines The advantage the simple machine gives to the user can be calculated.

A machine approaches a mechanical advantage of 1, when output forces roughly equal input forces.

Mechanical Advantage

MA = Fo

Fi

Output force (N)

Input force (N)

mechanicaladvantage

Mechanical advantage

What is the mechanical advantage of this new lever?

Torque and mechanical advantage What’s the mathematical relationship between torque and mechanical advantage?

MA = Output Torque ÷ Input Torque

Build different levers…

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

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?

Mobiles are levers!

GREAT STEM project!

Outcomes

Use science

Think scientifically

Communicate technical ideas

Teach all students

Be science conscious NOT science phobic

What questions do you have about Torque or Mechanical Advantage?