FORCES AND THEIR EFFECTS

Wednesday, April 19, 2023 1

FORCES AND THEIR EFFECTS

Unit 7KYear 7 Science


Indexintroduction

lesson 1: Are some magnets stronger than others?

lesson 2: What forces act on a parachute?

Homework task 2

lesson 3: How much do balls bounce?

lesson 4: Do rollers make it easier to drag heavy things?

lesson 5: Why is iron heavier than aluminium?

lesson 6: Are objects lighter under water?

lesson 7: Why are some toy cars faster than others?

lesson 8: Do things float better in salty water?

lesson 9: Is friction sometimes useful?

lesson 10: Do pulleys help with lifting?

Forces

• What are forces?• How do we measure forces?• How do we use forces in our

ordinary lives?• How do forces affect our lives?


What do all these terms mean?• FORCE: the influence that produces a

change in a physical quantity; "force equals mass times acceleration" (Newtons)

• POWER: the rate of doing work; measured in watts (joules per second)

• WORK: "work equals force times distance" • ENERGY: the capacity of a physical

system to do work (joules)



Introduction

http://www.westwightmiddle.iow.sch.uk/science.htm

Getting help

You will be loaned a study guide

Use our web site

This unit is all about FORCES

pushes, pulls and twists

Forces are measured in NEWTONS


Lesson 1

Are some magnets stronger than others?


Objectives and what I am looking for

• Learn about magnetic force

• Learn to list the key variables effectively

• Learn to evaluate the way you work

• Make careful measurements.

• Learn how to use the guide mats

• Make a proper variables list

• Record your results in a table


Equipment

• A variety of different magnets• 30 cm rules marked in mm• Steel ball bearings• Results tables• Level mats• Study guides (3 levels differentiated)


Are some magnets Are some magnets stronger than stronger than others?others?

Learn to list the key variables effectivelyLearn to evaluate the way you workMake careful measurements.

• Watch a demonstration of how to test.

• What are variables?

• Use whiteboards to list the variables.




Planning

1. Make a list of the key variables

2. Which variable will you test?

3. Which variable will you measure?

4. Which variables will you keep the same?

New page. Date and title in your book.



• Put the ball bearing on the table.• Move the magnet nearer to the ball

bearing.• How close was the magnet when the

ball started to move? Measure.• Record your results and try again with

a different magnet.



Are some magnets Are some magnets stronger than others?stronger than others?


Magnet How close was the magnet?

Let’s share our results

ObservationsState which magnet is the strongest according to your results.



Evaluation• How well did your test go? • Did you feel that your results were

accurate? • How could you have improved your test in

order to get more accurate results or results you could have been more sure of?


Work in pairs


Lesson 2

What forces act on a parachute?



Parachute video (it might work)


Equipment

• Digital camera• A football• Parachutes• Timers• Whiteboards, pens & erasers• Study guides (3 levels

differentiated)


OBJECTIVES& what I am looking for

• To learn about a force called DRAG

• To learn to draw force diagrams

• To learn how to mark forces on a diagram

• Make a diagram that clearly shows the forces that act on it.

• Write to describe which force is largest.

• Write to explain how you know.


How to mark force arrows on diagrams.

drag

thrust

weight

lift

New page, date & title.

Copy the diagram.

To learn about a force called DRAGTo learn to draw force diagramsTo learn how to mark forces on a diagram


Football

• We will go into the playground to watch a football and bring back a photograph.



Football photograph

• Trim and fix the photograph into your book.

• Use arrows and straight lines to mark:– Gravity– Drag To learn about a

force called DRAGTo learn to draw force diagramsTo learn how to mark forces on a diagram


Next bit…

• DVD video input: BBC Class clips


Plenary: What forces act on a parachute?

• Try a parachute in the lab from a height of Try a parachute in the lab from a height of exactly 2 exactly 2 metresmetres.

• NOW RECORD THIS ON YOUR GROUP’S WHITEBOARD• Decide what force pulls the parachute down.• Decide what force holds the parachute up.• Which of the forces was greatest? Explain how you know.


Work in pairs HOMEWORK



• The force that pulls the parachute down is…

• The force that holds the parachute up is.• Draw an accurate 2d diagram that shows

the parachute and the two forces acting on it.

• The force that was greatest was… I know this because…


IN YOUR BOOK


Finishing up

• Forces ‘Hammer & Feather on the Moon’. (Class Clips DVD)


Homework task 2

• Use your knowledge of DRAG to explain why sports cars are streamlined.

HOMEWOK SHEET


Use your knowledge of DRAG to explain why sports cars are streamlined.










Lesson 3

How much do balls bounce?


Getting started…

• Draw a ball falling. Think about its shape.

• Draw a ball that has hit the ground and is about to bounce back up. Think about its shape.


OBJECTIVES& what I am looking for

• How do forces make things bounce?

• Are my measurements accurate?

• Why is it important to repeat my tests?

• How can I use my scientific knowledge to explain?

• Be able to do a test and make accurate measurements.

• Be able to repeat measurements to check.

• Be able to clearly describe what happened.

• Be able to use your knowledge to explain how and why things happen.


Which forces make balls bounce?

1st bounce

2nd bounc

e


Equipment

• Clamp stand with clamp and boss.

• Metre rule.• Table tennis ball.• Results table.• Study guides.

Equipment

table tennis ball

metre rule

clamp stand


Resultstest number first bounce second bounce

1

2

3

4

5

6

7

8

9

10


Conclusion

• According to your results, describe what happened.

• Use your understanding to explain why the first bounce was more than the second bounce.


Something to think about…• The falling ball had kinetic

energy because it was moving. • The amount of movement got less

after the first bounce.• So, where did the kinetic energy

go?


Plenary & finishing off…

• Your group might be asked to read your conclusion.

• Copy your conclusion to your exercise book. Improve it as you go.

• Homework: Complete the conclusion in your book.


Forces & their effects: Lesson 4

Do rollers make it easier to drag heavy things?


Just for starters…

• Draw a picture of a bloke dragging a heavy rock.

• Draw a picture of the same bloke dragging a heavy rock using rollers.

•Can you show which one is the hardest work?


OBJECTIVES & what I am looking for• To learn how to

write why your test is fair.

• To learn how to make a useful bar chart.

• To extend your ability to explain why things happen.

• Know about control, independent and dependent variables.

• Write a useful prediction.

• Record your results accurately.

• Write to explain why things happened.

• Write an evaluation.


Equipment

FOR GROUP WORK:• Dowel rollers• Force meters• String• A brick• Study guiders• Results tables• Level mats


Key variables

INDEPENDENT VARIABLEThe variable I will test is…

DEPENDENT VARIABLEThe variable I will measure is…

CONTROL VARIABLESThe variables I will keep the same are…

Redraft into your exercise book.


Practical bit…

Use a board to protect your bench.

Test number How much force without

rollers?

How much force with

rollers?

1

2

3

4

5

RESULTS


Conclusion

• Produce a graph that shows these results clearly. [What should my graph look like?]

• Write to explain what happened in terms of forces and energy. [What should my work look like?]

• Plenary: Evaluate your test.


A clear graph

0

2

4

6

8

10

12

14

16

Without rollers With rollers

1

2

3

4

5

Forc

e (

N)

CONCLUSION PAGE


Model conclusionIf the brick is dragged along the ground, the rough surfaces lock together and make lots of friction.

All of the surface of the brick is touching the ground. The bigger the surface, the more friction there is.

It takes a lot of force to drag the brick.

If you use rollers, the rough surfaces do not lock together and so there is much less friction. So it takes much less force to pull the block.PREVIOUS PAGE


Forces & their effects: Lesson 5

Why is iron heavier than aluminium?


OBJECTIVES& what I am looking for• To learn the idea

of density.• To learn to

measure and compare different materials.

• You can measure mass in grams.

• You can measure volume in cm³ .

• You can record your results in tables.

• You can calculate the mass of 1 cm³ of each material.

Equipment

FOR GROUP USE• Metal blocks (materials kit) Iron,

brass, aluminium & lead HAZARDHAZARD• Electronic scales• Study guides



Stage 1

• What is the mass of each metal block? (Measure in grams)

• Make a table of your results.

metal mass g

iron

brass

aluminium

lead


Was this a fair comparison?

• Describe why your test is not fair.• Can you work out what the mass

would be if every block was 1 cm³?

iron

aluminium

lead

brass


What is the mass of 1cm3 ?

• Can you work out what the mass would be if every block was 1 cm³?

Material Mass (g) Volume (cm3)

Density (g/cm3)

iron

brass

aluminium

lead


What should your results be?Material Density (grams per cm3)

iron 7.87

brass ?

aluminium 2.7

lead 11.36


So…

Now you know which material was the most dense.

Check learning


Plenary: Any ideas?

Material Density (grams per cm3)

iron 7.87

brass ?

aluminium 2.7

lead 11.36

water?

Copper?

Wood?

Cheese?

Finishing up

•Save any computer work.•Equipment away please.•Give in your books.•Clear your table.•WASH YOUR HANDS!


Forces: Lesson 6

Are objects lighter under water?

Equipment

• Objects to weigh underwater• Forcemeters



OBJECTIVES& what I am looking for• To learn the idea of a

force called upthrust.• To learn how to

make accurate measurements of forces.

• To develop your ability to explain why things happen.

• To correctly mark forces on diagrams.

• You can draw a basic force diagram in 2D.

• You are able to measure force accurately using a force meter.

• You can use the computer to produce a useful graph that shows your results clearly.

• You can explain why forces cause things to be lighter in water.

• You can evaluate your test.


What forces?

dragthrust

weight

upthrust


The proper way…

gravity

upthrust

dragthrust


Instructions

• Use the study guide. Write the title & date.

• Write: What is the force that pulls down on the stone? [The force that… ]

• Draw the diagram in 2 dimensions showing the forces correctly.

• Use the equipment to find out if objects are lighter under the water. Repeat each test to get accurate results.

• Record your results in a table.


ResultsObject weight in air

(NEWTONS)weight under

water(NEWTONS)

Difference (NEWTONS)


Produce a spreadsheet using a computer. Use a formula to calculate the difference

column. Object weight in air

(NEWTONS)weight under

water(NEWTONS)

Difference (NEWTONS)

stone 3 2 =B2-C2

iron block 5 3½


Conclusion & evaluation

• Explain why the objects were lighter under water. Make sure you show your knowledge of forces.

• Evaluate your test.


Forces: Lesson 7

Why are some toy cars faster than others?

Equipment

• Toy cars• Wooden ramps• Clinometers• Stop watches



OBJECTIVES

• To learn why it is important to make lots of measurements.

• To learn how to explain why things happen.

• To learn about friction and drag.

• To do a fair test.• To learn why it is

important to make lots of measurements.

• To explain why a force called friction affects the speed of a car.

• To explain what happens to the energy.

• To calculate speed.


By the end of the lesson…

• Be able to peruse, choose and use the right equipment.

• Be able to list the variables.• Be able to write an explanation.• Be able to measure and calculate

speed.*


Force diagram

thrust

weight

road holds kart up

friction and drag


Forces: Lesson 8

Do things float better in salty water?

Equipment

• Hydrometers• Salty water• Very salty water• Tap water• A ball• Transparent fish tank



OBJECTIVES / OUTCOMES

• To learn about forces that act in different directions.

• To develop your ability to explain why things happen.

• You can peruse, choose and use the right equipment.

• You can measure accurately.

• You can explain why forces make this happen.

• You can evaluate your test.


Starter

Pushing a ball onto a bucket of water.

Key questions…• As I push the ball down, what

happens to the water?• Does the water have mass? Am I

lifting it?


As the ball is pulled down by gravity, the water is lifted.

The ball will go down until it balances the mass of the water it is pushing out of the way.


What if the ball was lighter?

What if the water was heavier?

How could you make the water heavier?


Input

• BBC DVD: Class Clips 1 / Materials & their properties / Compounds & mixtures / 5 Mixtures


SALTY WATER

TAP WATER

VERY SALTY WATER

Wooden dowel

blob of plasticine

water

diagram

Water type Height of hydrometer

(mm)

Density of water

Very salty

Salty

Tap water (no salt)

•Use the same hydrometer every time.

•Measure how high the hydrometer floats (in mm from the surface of the water to the top of the dowel).


Finishing up

• Why does the hydrometer float better in very salty water? Write to explain why in terms of forces.

• Evaluate your test.


Forces Lesson 9

Is friction sometimes useful?


OBJECTIVES / OUTCOMES

• To learn how friction is sometimes a useful force.

• To learn where friction forces happen.

• To learn how to add labels and captions.

• Your two diagrams show that you know where high friction is important.

• Your two diagrams show that you know where low friction is important.

• You can write useful captions.

Equipment

• Video: Cycling crazy



Activities

• Video: Cycling crazy• High friction and low friction (use

study guide)



Rounding up

• Your two diagrams show that you know where high friction is important.

• Your two diagrams show that you know where low friction is important.

• You can write useful captions.


Forces Lesson 10

Do pulleys help with lifting?

Equipment

• Pulley sets• Hang on masses• Forcemeters• 1kg masses• String



OBJECTIVES/ OUTCOMES

• To learn that pulleys are helpful for lifting.

• You can work as a team to set up the test.

• You can use a forcemeter to measure the pulling forces.

• You can record your results in a table.

• You can write to describe what you noticed.

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FORCES AND THEIR EFFECTS

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