Key Questions: What is a newton? How does a lever work? What is the relationship between force and distance in a simple machine? What factors.

Key Questions:

What is a newton?

How does a lever work?

What is the relationship between force and distance in a simple machine?

What factors balance a lever?

Performance Objectives

Describe how a lever works.

Identify the relationship between force and distance on a lever.

Apply the concept of mechanical advantage to 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!

FORCESForces have two important properties: strength (magnitude) and direction.

In the English system of units, the strength of a force is measured in pounds.

When you measure your own weight in pounds, you are measuring the force of gravity acting on your body.

The NEWTON

In the metric system, the strength of a force is measured in newtons (N).

A quarter-pound hamburger has a weight of about 1 newton (1 lb = 4.448 N).

Zero the Spring ScaleIn the metric system, the strength of a force is measured in newtons (N).

Gravity and weight The force of gravity on an object is called weight.

Mass and weight are not the same thing!

Gravity and weight

A 10-kilogram rock has a mass of 10 kilograms no matter where it is in the universe.

A 10-kilogram rock’s weight however, can vary greatly depending on where it is.

Simple Machines

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

Simple machines change the magnitude or direction of forces

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

CPO Lever – First Class All The Way

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?

Four Variables in a Lever

Amount of Input Force

Amount of Output Force

Length of Input Arm

Length of Output Arm

Lever Challenge Hang weights from

the lever and get it to balance.

Use only 3 strings, one string per position and string MUST have weight.

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

Lever Challenge

Lever Concept 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.

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)

=

TOY Engineers

Allow time for students to brainstorm possible design ideas and to plan how they will construct their toys.

Once students have built their toys, let them share their creations with the class.

Outcomes

Use science

Think scientifically

Communicate technical ideas

Teach all students

Be science conscious NOT science phobic

What questions do you have about the CPO Levers?