Lesson D4: Working with Machines

Key Ideas     Unit Checklist

  Video Lesson

What is work and how do we calculate work? Watch this video to learn more. 

 
 

  Lesson D4: Working with Machines


Figure D.2.4.1 – Pulleys can be used to change the direction of force.

Figure D.2.4.2 – Depending on the pulley arrangement, machines can reduce the force needed to lift. 


Figure D.2.4.3 – Several pulleys can drastically change the direction of force.
Reading and Materials for This Lesson

Science in Action 8
Reading: Pages 287–292

Materials:
Piece of scrap wood, hammer, nail, screw, screwdriver.

Weightlifting Machines

People lift weights as an exercise to strengthen their muscles and bones. There are two ways of lifting weights. People can directly lift weights. People can also lift weights using a weightlifting machine.

It takes the same amount of work to lift a weight by hand or with a machine. Weightlifting machines sometimes use pulleys to reduce the force needed to lift a weight. Weightlifting machines also change the direction of the weight’s force, which allows a person to work different muscle groups.

Because they often require less force, weightlifting machines are a safer way for people to exercise without hurting themselves, especially for beginners or older people.

  Try It! 

Removing Nails and Screws

Try this activity to observe the force and distance needed to pull nails and screws out of wood. 

Materials: 
  • Piece of scrap wood
  • Hammer
  • Nail
  • Screw
  • Screwdriver

This activity involves a hammer and nails. It must be completed with the supervision of an adult. DO NOT attempt this activity by yourself.

Hammering and removing sharp nails can hurt you or others if you are not careful.
Download:

DOWNLOAD this document. It provides a table for you to record your observations. It also provides space for you to answer the questions later in this activity.

Instructions:

  1. Hammer the nail into the piece of wood. Leave about 1 cm of the nail sticking out of the wood.

  2. Try pulling the nail out of the wood directly with your hand. Record the following observations in a table:
  • What do you observe about your force input?
  • What do you observe about the distance your hand moves?
  • Did you do work?

  1. Use the claw of the hammer to pull the nail out of the wood. Record the following observations in a table:
  • What do you observe about your force input?
  • What do you observe about the distance the hammer moves?
  • Did you do work?

  1. Turn the screw into the piece of wood. Leave about 1 cm of the screw sticking out of the wood.

  2. Try turning the screw out of the wood directly with your hand. Record the following observations in a table:
  • What do you observe about your force input?
  • What do you observe about the distance your hand moves?
  • Did you do work?

  1. Use the screwdriver to turn the screw out of the wood.
  • What do you observe about your force input?
  • What do you observe about the distance the hammer moves?
  • Did you do work?

Observations:

Download the handout for this activity and fill in the table as you proceed through the instructions.



Questions: 

Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.

You did work in the situations when the nail and screw moved. These situations were when you used the hammer claw to remove the nail and the screwdriver to remove the screw.
You did not do work in the situations when the nail and screw did not move. These situations were when you tried to remove the nail and screw by hand.
The hammer claw is a first class lever.
It was difficult to pull the nail out of the wood by hand, because your hand could not apply enough force to do the work. Your work input to the hammer moved the hammer handle a larger distance with less force. Your work input is the same as the work output of the hammer. However, the short hammer head lever moved a smaller distance, which meant it applied a greater force to the nail.
The screwdriver is a wheel and axle.
It was difficult to turn the screw out of the wood by hand, because your hand could not apply enough force to do the work. The wheel handle of the screwdriver is bigger than the axle shaft of the screwdriver. Your work input to the bigger screwdriver handle turned the handle a greater distance, with less force. Your work input is the same as the work output of the screwdriver. The smaller screwdriver shaft turned a smaller distance, which meant it applied a greater force to the screw.

Lesson Activity

Calculating Work

 Problem:

In this lesson activity, you will explore how force and distance affect work.
 
Download:

DOWNLOAD this document. It provides a table for you to record your observations. It also provides space for you to answer the questions at the end of the activity.

Instructions:

  1. Click here to open this box-lifting simulation in your browser.

  2. Note that the person in this simulation can apply a maximum force of 600 N. The simulation also assumes that there is no friction between the box and the ramps.

  3. Click the setting for 1 m. You should see the person lift a 50 kg box up 1 m onto the back of a truck. If you want to see any simulation again, click the “replay” button.

  4. The force needed to move the load is recorded in the table for you. Calculate and record the work done by the person moving the box into the truck. Record your answer in the observations table. Show your work as well as your final answer. Remember, work equals force times distance. (W = F x d)

  5. Repeat Steps 3 and 4, for ramps of 1.4, 2, and 3 meters.

  6. Now click the “double load” box so the person must move two boxes onto the truck.

  7. Repeat Steps 3 to 5 using the double load.

Observations:

Download the handout for this activity and fill in the tables as you proceed through the instructions.

Lifting One Box
*Note – maximum force the person can apply is 600 N
Lifting Two Boxes
*Note – maximum force the person can apply is 600 N



Analysis Questions:

Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.

The work done to lift one box is the same for all ramps and for lifting the box straight up, which is approximately 500 J.
The work done to lift two boxes (double load) is the same for the 2, and 3 m ramps, which is approximately 1000 J. The person could not apply enough force to move the double load up 1 m or up the 1.4 m ramp, so 0 J of work was done.
Increasing the distance of the ramp does not affect the amount of work needed to lift boxes. The work done to lift boxes against gravity is the same lifting straight up or for any length of ramp.
Increasing the distance of the ramp reduces the amount of force needed to lift boxes. Longer ramps required less force to lift boxes.
The person was only capable of exerting 600 N to lift objects. Lifting two boxes straight up, or using the 1.4 m ramp, required too much force. The person could not exert enough force, so the boxes were not moved from their starting position, so no work was done.
Using a 2 meter ramp required a force of 500 N to be exerted on the boxes. Since the person was capable of exerting up to 600 N of force, they had enough force to push the boxes up the ramp into the truck.

  Connections 

Figure D.2.4.4 – A seesaw looks like the class 1 levers we see in diagrams.
Figure D.2.4.5 – Scissors are made up of a pair of class 1 levers connected at the fulcrum.

Connections – Math
>> Lever Calculations

The position of a fulcrum on a first class lever does not have to be in the center of the lever. Changing the position of the fulcrum changes the amount of force on each end of the lever.

Watch this video to learn more about lever length and how it affects the lever force.

 
 
Figure D.2.4.6 – Horses used to power many machines.
Figure D.2.4.7 – Car engines are still measured in horsepower.


Figure D.2.4.8 – Electric cars are efficient – with half the horsepower, they are as fast as gasoline engine cars.
Horsepower

In the past, people used horses to do work. Horses pulled carriages, dragged farm equipment, and turned mill wheels. When the steam engine was invented, people didn’t understand how powerful it was. To sell more machines, the steam engine’s inventor described it in terms of “horsepower”. This is a description of how many horses it would take to do the same amount of work in a period of time.

Power measures how much work can be done in a certain amount of time, or the rate of work. People still use horsepower to describe modern engines in cars and other machines. Small compact car engines have a horsepower of approximately 100. That means it would take 100 horses to pull a small car driving at high speed. For comparison, sports cars often have a horsepower between 300 and 400. They can accelerate faster and drive at faster speeds.



  Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.

Unit D Lesson 4 Self-Check

Instructions


Complete the following 6 steps. Don't skip steps – if you do them in order, you will confirm your understanding of this lesson and create a study bank for the future.

  1. DOWNLOAD the self-check quiz by clicking here.

  2. ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.

  3. COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.

  4. REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.

  5. SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.

  6. CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!

Be a Self-Check

Superhero!



Self-Check Quiz Answers

Click each of the suggested answers below, and carefully compare your answers to the suggested answers.

If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.

Work equals force times distance (W = Fxd). The force of 400 newtons multiplied by a distance of 2.00 meters equals 800 joules of work.
The man is not actually doing work. You only do work if you make an object move. The man is exerting a lot of force, but he is not able to produce enough force to move the car. A more accurate statement would be “I’m exerting a lot of force!”.
Work equals force times distance (W = Fxd). In order to do 1500 joules of work, the piano movers need to use a force that can be multiplied by 3.00 meters to equal 1500. 500 x 3.00 = 1500, so the piano movers used 500 newtons of force.
We know that the amount of work needed to move the couch does not change.  The first thing we need to find is how much work it takes.  So, Work = Force x distance When we are moving it straight up into the house we would say that 
W= F (in newtons) x d (in meters)
W= 600N x 2m.  
W= 1200 Joules 
*The question tells you that you have to use 600N of force and that you are moving it up 2meters.  Right?  Does that make sense?  

OK, now you use the information you just figured out to see how much force you will use when using the ramp.  The amount of work doesn't change- you still have to use 1200J of force.  The thing that changes is the distance and so that affects the force exerted. 
W= Fx d
1200= F x 4m
1200/4 =F
300N= F

So, you will exert 300 Newtons of force to move the couch up the ramp.  
When you need to do work, you do the same amount of work with the machine or without the machine. A machine makes work feel easier because it enables you to do the work with less force, by increasing the distance of the work.