Grade 8 Forces Presentation

Grade 8 Science

Forces and Their Effects

http://commons.wikimedia.org/wiki/File:Jal.747.newcolours.arp.750pix.jpg

The Solar System

What keeps the planets moving?

http://commons.wikimedia.org/wiki/File:Solar_sys.jpg

Forces

A force is a push or a pull.

Forces are measured in Newtons, after Isaac Newton.

What force is required to:
1. open a drawer
2. untie a shoe lace
3. turn on a tap (difficult)
4. lift your pencil case.

http://commons.wikimedia.org/wiki/File:Isaac-newton_1.jpg

Gravity

Gravity is a very weak but important force.

Gravity pulls everything together.

We notice it as pulling us down towards the Earth.

Gravity also pulls the Earth towards the sun.

http://www.icteachers.co.uk/children/sats/gravity.htm

Mass and Weight

Mass measures quantity of matter. It is measured in kilograms (kg).

Weight measures the force of gravity. It is measured in Newtons (N).

Short task:
Measure the mass and weight force of four items in the laboratory.

ItemMass (kg)Weight (N)

Find something with a weight force of 1 Newton.

Mass and Weight Relationship

The relationship between mass and weight is:
Weight (Newtons) = mass (kilograms) * 10We MUST convert grams to kilograms first.

10 is the value of gravity on Earth.

Calculate the weight force of a 60kg person, an 800 kg car and a 50 gram feather.

8A got to here 23 August

Gravity on Earth

Weight = mass * 10 - on Earth only.

In space, weight force is nearly zero.

Every place in the universe has its own number for gravity.

1. Calculate the weight force of a 60kg person on The Moon (1.7), Mercury (4), or Jupiter (2.6).
2. Explain why things weigh more on Jupiter.
3. What is wrong (scientifically speaking) with saying: I weigh seventy kilograms.

Quick Review

Explain the difference between mass and weight, in your own words.

What is the weight of a 2kg object (on Earth)?

Calculate the weight of a 200g object (on Earth).

Aristotle's Theory of Motion

Aristotle was a Greek philosopher
who lived around 384-322 BCE.

He developed a theory of motion (=???) which survived about 2000 years, until about 1600.
Who disproved Aristotle's theories?

Stars (including planets) were fixed on large spheres, which moved in perfect circles around the Earth, and explained the movement of stars in the sky.

There were about 50 spheres moving in total.

http://commons.wikimedia.org/wiki/File:Aristotle_Altemps_Inv8575.jpg

http://tutorsincalgary.com/science-tutor-calgary.jpg

Please load the image shown at the URL below (it cannot be included in my presentation due to copyright).

The Four Elements

Everything under the moon (on Earth) was made of a combination of five elements: earth, air, fire and water.

Fire was the lightest, then air, then water, then earth.

Everything, if left alone, would move to its natural state and stop moving.

Iron was mostly Earth, whereas wood had some earth, some water and some air.

The Four Elements

What's in these?

http://commons.wikimedia.org/wiki/File:Elliotts_car.jpg

http://commons.wikimedia.org/wiki/File:Balloons-aj.svg

http://commons.wikimedia.org/wiki/File:Air_.pollution_1.jpg

Violent Motion

Violent motion was the opposite of natural motion.

Violent motion is caused by living things applying a force to something. When the force stops, the motion stops.

http://upload.wikimedia.org/wikipedia/commons/a/a2/Pushing_van_together.jpg

What Can't it Explain?

http://godgrown.net/blog/2011/01/12/as-easy-as-the-arrows-job-in-archery/

Questions

1. Explain Aristotle's theory of motion. Give two examples of phenomena it can explain well, and one it can't.
2. Explain Aristotle's views were believed (in the west) for about two thousand years.
3. Suggest a reason why Newton's laws were accepted immediately by the scientific community.
4.Use Newton's laws of motion to explain why an arrow flies so far after being released from a stretched bow. Why doesn't it fly forever?
5. Research: Which famous scientist first challenged Newton's laws of motion? Why do we still teach it, even though Newton's laws are technically not correct?

Falling Objects

Aristotle believed that heavier objects would fall faster, but never tested it.

Galileo Galilei is famous for being the first in recorded history to test whether heavier objects actually fall faster.

Conclusion: all objects fall at about the same speed.

http://commons.wikimedia.org/wiki/File:Leaning_Tower_of_Pisa.jpg

Newton's Laws of Motion

Isaac Newton devised three laws of motion which explained how all objects move, from particles of air to planets in the Solar System.

They linked is law of Gravity with Kepler's Laws of planetary motion.

http://commons.wikimedia.org/wiki/File:Newton_-_Principia_(1687),_title,_p._5,_color.jpg

Newton's First Law

All objects will continue to move at constant speed and direction unless an unbalanced force acts on them.

http://commons.wikimedia.org/wiki/File:Voyager_spacecraft.jpg

Why do Cellphones Fly out Windows?

Forces: The Basics

A force is a push or a pull.

A force has a size (in N________) and a direction.

A force can be drawn as an arrow. The length of the arrow represents its size and the direction of the arrow represents the direction of the force.

A force can cause an object to change its speed (a_________), change its direction or change its shape.

Balanced Forces

http://commons.wikimedia.org/wiki/File:Paperback-stack.png

Car (stationary)


Car (moving)

http://commons.wikimedia.org/wiki/File:2009-03-11_Beat_up_car_driving_in_Durham.jpg

Bookwork

Integrated Science 2, pages 42, 43, 44 (all questions).

Note: the force of a fluid (eg water or air) pushing upwards on something (page 43 top left) is called a b_______________ force.

http://commons.wikimedia.org/wiki/File:Isarfloss.jpg

http://commons.wikimedia.org/wiki/File:Hot-air-balloon.jpg

The Cable Car

http://en.wikipedia.org/wiki/Wellington_Cable_Car

http://en.wikipedia.org/wiki/Wellington_Cable_Car

http://en.wikipedia.org/wiki/File:Duquesne_incline.jpg

Hakone Ropeway

http://commons.wikimedia.org/wiki/File:1_hakone_ropeway_2010.jpg

Water Balance Railway

http://upload.wikimedia.org/wikipedia/commons/7/76/Funicular%2C_Centre_for_Alternative_Technology%2C_Machynlleth_-_geograph.org.uk_-_829550.jpg

Integrated Science book 2

Questions page 42-43

Newton's Second Law

If an unbalanced force acts on an object, it will cause it to accelerate.

Acceleration is a change in speed or a change in direction.

Force = mass * acceleration.


Newton's Third Law

Every force creates an equal force in the opposite direction.

http://commons.wikimedia.org/wiki/File:Skaters_showing_newtons_third_law.svg

http://commons.wikimedia.org/wiki/File:Recreational_kayak.jpg

http://commons.wikimedia.org/wiki/File:Model_rocket_launch_2_(Starwiz).jpg

Newton's Wheeley Chairs

1. Two people must push off each other so that one person moves backwards and the other stays still.
2. Two people must be pushed into each other (collision) so that both people stop.
--> Equal and opposite forces cause each other to stop.

Questions

1. Explain Aristotle's theory of motion. Give two examples of phenomena it can explain well, and one it can't.
2. Explain Aristotle's views were believed (in the west) for about two thousand years.
3. Suggest a reason why Newton's laws were accepted immediately by the scientific community.
4.Use Newton's laws of motion to explain why an arrow flies so far after being released from a stretched bow. Why doesn't it fly forever?
5. Research: Which famous scientist first challenged Newton's laws of motion? Why do we still teach it, even though Newton's laws are technically not correct?

Speed

Speed is a measure of how fast something moves.

Units are m/s (or cm/s, km/s etc).

Eg. Cliodhna is running during PE. After 20 seconds she has run 120. What is her speed?

1. Calculate how far Cliodhna would run in one minute (using the speed from the previous example).

2.A. Moena is swimming at 2m/s. How long will it take her to swim a length of a swimming pool (25m)?

B. How far can Moena swim during a 45 minute PE class if she swims for the whole class?

Measuring Walking / Running Speed

Work in groups of 4 or 5.

Measure the speed of a person walking and running. (It does not have to be the same person walking and running).

Use a distance of 5-10 metres.

Repeat each set at least twice, and take the average of all trials.

Present your results in a summary.

The Investigation

Aim: To determine how fast _____ walks and ______ sprints.

Apparatus: stopwatches, meter rulers

Prediction: ________ will walk at _____ m/s and _________ will sprint at _____ m/s.

Method:
1. Measure a suitable distance for someone to walk, and sprint.
2. Arrange a system for ensuring that the timing is accurate.
3. Record at least three trials, and calculate the average speed for walking and running.

Results and Conclusion

__________ Walking

__________Running

Trial numberDistance (m)Time (s)Speed (m/s)

123Average speed

Trial numberDistance (m)Time (s)Speed (m/s)

123Average speed

Measuring the Speed of Cars

How will we measure the speed of cars along the road outside YIS first thing on Monday?

Equipment: tape measures, stopwatches

Work in group of 3, 4 or 5.Safety:

No one is allowed on the road at any time (except crossing it at the proper crossing).

Signals should not distract cars.

Write up a plan as a google doc for each group, and share it with me. It should include the names of each member of the group, and a detailed plan. It might help to have a table printed ready to go.

1. Compare your results to others in the class. Who is the fastest a) runner? b) walker?

2. The result obtained is an average speed. Explain what is meant by an average speed. You may need to do some research for this question.

3. Two years ago in Berlin, Usain Bolt from Jamaica set the world record for the 100m sprint, coming in at 9.58s. Calculate his average speed, and compare it to the fastest student in the class.
4. A. Convert your group's walking and sprinting speed to km/h. This may requires some thought.
B. Use this, and google maps (directions) to calculate how long it would take to walk AND run to
i) your home
ii) Tokyo tower

Friction

Friction is a force which opposes motion.

It is always in the opposite direction to motion.

Friction can occur between two surfaces. Air friction (drag) occurs when an object moves in the atmosphere (or another fluid).

http://www.physics4kids.com/files/art/motion_friction1_240.jpg

Parachute

What factors would determine how strong air resistance is?

http://commons.wikimedia.org/wiki/File:Ronde_parachute.png

Streamlining

Streamlining is the shaping of a (usually fast-moving) object to minimise air resistance.

http://commons.wikimedia.org/wiki/File:Shinkansen_Nozomi_in_Tokyo.jpg

Acceleration

Newton's ____ law refers to acceleration.

Acceleration is a constant change of speed.
eg. Something starts at rest. After 5 seconds, it is travelling 10m/s. After 10 seconds, it is travelling 20m/s. How fast will it be travelling after 20 seconds?

The acceleration of the object is __________.

Terminal Velocity

Friction increases as speed increases.

Eventually the forces of friction and gravity are equal and opposite, so cancel each other out.

Newton's first law then applies, and the object keeps moving in the same speed and direction (downwards).

The fastest speed something can fall is called its terminal velocity.Factors which affect terminal velocity:

Skydivers reach a terminal velocity of 190km/h (belly first) or 300km/h (head first).

http://commons.wikimedia.org/wiki/File:Skydiver_on_back_of_partner_and_giving_thumbs_up.jpg

Bookwork

Page 145 (Spotlight Science 9)

There is no need to use the particle theory for question 4 (but use it if you've learnt it!).

A hovercraft is shown below.

http://en.wikipedia.org/wiki/Hovercraft

Motion Graphs

A motion graph shows how something moves in relation to time. Time is always on the X axis. At grade 8, we cover distance-time graphs and speed-time graphs.

Introductory exercise:
Consider the parachute we made last time. SKETCH a graph of its speed against time from the moment it is dropped to the moment it hits the ground. Assume there is minimal wind blowing.

Time (seconds)

speed
(m/s)

Time (seconds)

Speed
(m/s)

0Parachute dropped

5
Parachute hits the ground

The Falling ParachuteThe parachute took 5 seconds to reach the ground.

Time (seconds)

speed
(m/s)

0Parachute dropped

5
Parachute hits
the ground

The Falling Parachute

1. Where is each of the following on the graph above:
Stationary, constant (slow) speed, constant (fast) speed, acceleration, deceleration

2. If this shows a car's motion
a) At which point is thrust greater than friction?
b) At which point is friction greater than thrust?
c) Are there any forces acting on the car at point a? If so, what?
d) Are there any forces acting on the car at point b? How can you tell?

Time (seconds)

speed
(m/s)

0

a

b

c

d

c

e

Distance Time Graphs

Distance time graphs show how far something has moved since the beginning of the measurement.

Time (seconds)

0Parachute dropped

5

The Falling Parachute

dis
tance (m)

0

3.5

Time (seconds)

0Parachute dropped

5

The Falling ParachuteThe parachute fell 3.5 metres.

dis
tance (m)

3.5

0

Bookwork

Page 146-147

Motion Graphs

Motion = movementA motion graph is used to show how something moves, and how its movement changes over time. It can show: whether an object is stationary or moving

an object's speed.

if and how its speed is changing (acceleration or deceleration).A motion graph can show all of the above on the same graph.

Types of Motion Graphs

Time always goes on the x axis.

A distance-time graph shows how far something has travelled on the Y axis.

Distance can not go backwards.

A speed-time graph shows how fast something is moving on the Y axis.

Bernie Walking at 1m/s

0 2 4 6 8 10Time (seconds)

Distance (m)

8

6

4

2

0


Speed (m/s)

8

6

4

2

0

Sammie walking at 2 m/s


Distance (m)

8

6

4

2

0


Speed (m/s)

8

6

4

2

0

Omer Accelerating

In the first second, he travels one metre per second.
In the second second, he travels at two metres per second.
In the third second, he travels at three metres per second.

How would we describe Bernie's motion?


8

6

4

2

0

Speed (m/s)

8

6

4

2

0

Distance (m)


Crocodile Physics

Load Crocodile Physics.

Work through Velocity-Time Graphs then Distance Time GraphsCopy and complete the following table (without using what we did last time):

MotionSpeed-timeDistance-time

stationaryConstant (non-zero speed)accelerationdeceleration

Note for the blog: 8C we will do this slide next week (starting 19th)

Motion Graphs Challenge

Use a spreadsheet (OpenOffice recommended, but any other is fine) to draw a distance-time graph and a speed-time graph for a train (any one of local, express etc) from Motomachi Chukagai to Shibuya.

Start from time = 0 when the train departs.

Tools: www.hyperdia.com

If you have a smartphone (and it's ok if you don't) install a GPS speedo and (as an extension) an accelerometer.

Note for the blog: 8C we will do this slide next week (starting 19th)

How long to drive to Shibuya?

According to google, it is 40km away.

How long will it take to drive there? What do we need to know?

What is 'Google's' average speed in km/h and m/s?

Source: Google Maps

Average Speeds

Consider the following journey? What is the average speed for?
a) the first 10 seconds?
b) the first fifty seconds?
c) the last fifty seconds?
d) the whole journey?

Estimate the instantaneous speed after 25 seconds.

Time (seconds)Total distance covered (m)

00

1050

20150

30250

40350

50500

60600

70650

80690

90700

100700

Source: Google Maps

Average verses Instantaneous Speed

Instantaneous speed is the speed something is going at any time. It is like reading the speedometer on a car.

http://commons.wikimedia.org/wiki/File:Tachometer_service_oil.jpg

Which is more Useful?

For safety (driving)?

When working out how long it will take to get somewhere?

Source: Google Maps

The Train to Shibuya
(8A Only)

Complete a distance-time graph (X-Y Scatter graph) for your journey to shibuya.

Use your spreadsheet to calculate the average speeds for each leg of the journey, and for the whole journey.

Hard: Sketch (either using a drawing tool on the graph, or by printing it, what the line on the graph might look like. Hint: think acceleration and deceleration: approximately how long does it stop for at each station?

Share your document with me.

Trains to Shibuya can reach speeds of over 100km/hr. Explain why your answers are so much lower than this.

http://commons.wikimedia.org/wiki/File:Inside_of_Yokohama_Municipal_Subway_10000.jpg

Crocodile Physics

Load Crocodile Physics.

Work through Velocity-Time Graphs then Distance Time GraphsCopy and complete the following table to DESCRIBE (not draw) the motion in words.

MotionSpeed-timeDistance-time

stationaryConstant (non-zero speed)accelerationdeceleration

The Essay

For this assessment task, you will need to research how Forces, Simple Machines and/or Magnetism has caused a particular problem in Japan or another country of your choice. It needs to be written as an essay and referenced using MLA format.For this assessment task, you will need to research how Forces, Simple Machines and/or Magnetism has caused a particular problem in Japan or another country of your choice. It needs to be written as an essay and referenced using MLA format.

MLA Referencing

It is very important for academic honesty in all study from middle school students to professors doing research to cite references properly.

If we read a random book, what do we need to say about the book so that someone else can find it?

Author, Title, Publication Info, Date

BookNorthedge, Andy. The Good Study Guide. 2nd ed. Milton Keynes: Open University, 2005.
Book with more than one authorCohen, Louis, Lawrence Manion, and Keith Morrison. Research Methods in Education. 6th ed. London: Routledge, 2007.
Chapter in a bookDovey, Jon. "Reality TV" The Television Genre Book. Eds. Glen Creeber, Toby Miller & John Tulloch. London: British Film Institute, 2001.


Journal articleBlack, Sharon. "Harry Potter: A Magical Prescription for Just About Anyone." Journal of Adolescent and Adult Literacy 46.7 (2003): 4.
Newspaper articleShepherd, Jessica. Smoothie transition: is it really goodbye to the student union bar and hello to mango energisers and campus gyms? The Guardian. 21st August 2007: 6FilmBlair Witch Project. Dir. Daniel Myrick and Eduardo Sanchez. Artisan Entertainment , 1999TV programmeState of play. Child Of Our Time. Victoria Bell. BBC. 2005


Web pageAuthor, last name first. "Webpage title." Website title. Date published/updated. Organization/publisher. Date accessed. < URL >

Daimon, Sayuri. Tohuku. Students Share Tales of Disaster on Global Stage. The Japan Times Online. 22 September 2011. The Japan Times. 23rd September 2011. http://search.japantimes.co.jp/cgi-bin/nn20110922f1.html Sometimes not all the information will be available; this does not matter.

http://www.studygs.net/citation/mla.htm

Pressure

Why does a sharp knife cut and not a blunt knife?

Why does a pin prick but not a finger?

Why does a chair leave marks
in the carpet?

http://commons.wikimedia.org/wiki/File:Knife_01.JPG

http://commons.wikimedia.org/wiki/File:Dwie_pinezki_(ubt).JPG

http://www.inspectapedia.com/interiors/StainInterior040DJFs.jpg

Pressure

Pressure occurs when a force is applied to an area.

The higher the pressure, the more damage a force will do to the surface.

Pressure is measured in Newtons per square metre(N/m2), or Newtons per square centimetre(N/cm2).

One N/m2 is called one Pascal, after the French genius Blaise Pascal.

Sample Problem 1

A box has a surface area of 0.5m2 and a weight of 80N. Calculate the pressure it exerts on the ground.

Sample Problem 2

The square prism below has a length of 1m and a width and height of 20cm, and it has a mass of 2kg. Calculate the pressure in Pascals it exerts on the ground when:
a) It is lying flat on its side as shown.b) It is standing tall.

Sample Problem 3

A 60kg person sits on a chair with their feet off the ground. The part of them in contact with the chair has a surface area of 600cm2. Calculate the pressure on the chair from the person sitting on it.

Pillows

Why is a soft pillow more comfortable than a brick floor?

http://commons.wikimedia.org/wiki/File:Body_pillow.jpg

http://commons.wikimedia.org/wiki/File:Worn_floor_-_geograph.org.uk_-_771522.jpg

How much weight will the balloon take before it pops?

There are 25 (rather blunt) nails.

NameWeight (g or kg)Name Weight (g or kg)

CliodhnaAsukaEmmaMahaadMelanieMitchellSatokaBenjaminRinaTomoCarolinePatrikChristinaTakumiWilliam WWilliam X

The Bed of Nails

In your notebooks, write a paragraph to explain why it doesn't hurt to lie on it. Also explain why is it necessary to lie down gradually, instead of standing on it first?

http://entertainment.howstuffworks.com/arts/circus-arts/bed-of-nails.htm

Bookwork

Page 151 (all questions)

Then continue with assignments.

Speed Revision

How long will it take to walk from here to North Star?

Assume I walk at 3 m/s and run at 7 m/s.

Source: Google Maps

Pressure

Air and water particles move around and push on everything around them. This is called pressure.

As the temperature of the liquid or gas increases, the particles move faster, increasing the pressure.

Air and water pressure increases as depth increases, because the pressure needs to support more weight on top.

The air pressure at sea level is about 100 000 Pa. This means that a cubic metre could support a weight of __________kg if there were no air pressure from above.

Pressure in Fluids

https://commons.wikimedia.org/wiki/File:Aquarium_empty.svg

A Nice Simulation

http://htwins.net/aps/

Why doesn't it explode?

Sucking Liquid Up A Straw

When we suck liquid up a straw, we don't suck it up. We suck the air out of a straw, and the atmosphere pushes the liquid up the straw.

Would it be possible to suck water up a straw on the moon?

http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/forceandpressure/appatmosphericpressure.html

Questions

Explain why the can was crushed in the water.

Explain why pressure around us is so high, but we cannot feel it.

Explain why it is not possible for humans to swim too deep.

Given that atmospheric pressure is about 100 000 Pa, show that a square meter could support 10000kg (about 15 cars).

Calculate the weight force on 1cm2 of air at sea level, assuming the atmospheric pressure above.

Hydraulics

Pascal's Law states that the pressure is the same anywhere in a fluid (except when depth changes).

Pressure = Force / Area.

Force =

The force is the same everywhere in a fluid.

A larger area makes a greater force.

Machines apply this principle to lift heavy objects. This is known as hydraulics.

http://home.wxs.nl/~brink494/hydr_e.htm

Siphon

Siphoning is making a liquid flow briefly uphill and then end up below where it started.

Please see this image for the idea but ignore the measurements on it as these are beyond G8 level:http://www.pump-zone.com/images/stories/piping/siphons%20and%20effect%201.jpg

Questions

1. Explain how hydraulics can be used to lift very heavy objects.

2. A large car has a mass of 1000kg and sits on a hydraulic lift with an area of 2m2. The lever has an area of 0.5m2.. Calculate how much force will be required to lift the car.

Diagrams deleted but unnecessary to answer the questions.

Youtube Video

http://www.youtube.com/watch?v=YlmRa-9zDF8&feature=related