Grade 9 Physics

?

Introduction Surveys

Some people have already done them, but they may have changed. So please do a new one
- thank you.

Mind Map / Brainstorm:
What is Physics?
Is it useful, and if so why?
What do you know about it?
What would you like to learn?

Sculpture: Use half a packet of clay to make something which symbolises Physics.

PHYSICS

Physics is the study of the laws of the universe.

Other Sciences often apply the laws of Physics, but to think of them this way is often pointless.

Physics came out of Astronomy, which is the oldest academic discipline.

This year we will cover mechanics (how and why things move), waves, light (including sight) and heat (including climate change).

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

Housekeeping

Welcome to the first year of MYP Grade 9 Science!

Textbooks
- none as yet. We will use the same textbooks as Grade 9s last year, and may issue them further into the course.

Any questions?

Sculptures

Show and Tell :)

Mathematics

The Book of Nature is Written in the Language of Mathematics.

-Galileo Galilei (image from Wikipedia)

Scientific Notation

Scientists often use scientific notation / standard form.

How comfortable are you with this.

Example Problems
1. Write ten million in scientific notation.
2. Write 4.3 * 1012 as an ordinary number.3. What is 4*1012 / 2*109?

Metric Prefixes

1 megaphone1 microphone2 kill a
mockingbird1 decacards1 microfiche

106 phones = 10-6 phones = 2000 mockingbirds =
10 cards = 10-6 fish =

More Metric Conversions

10-2 mental 1012 bulls10-12 boos10 millipedes106 aches

le Systme international d'units
(SI Units)

Units used to be problematic, with every country or group having their own, often inconsistent.The Metric system was developed in France after the revolution, and was officially adopted in France in 1779.SI Units became the official worldwide units in a conference General Conference on Weights and Measures in 1971. There are three countries which havent adopted them: Burma (Myanmar), Liberia and the USA.

Quantities and Units

A quantity is something which can be measured. For example: _______________

___________________________________.

Quantities are measured in units. Most (all?) quantities have multiple units for the same thing, and this can be problematic.

The Mars Climate Orbiter crashed because the Europeans and Americans used different units in its programming.

http://upload.wikimedia.org/wikipedia/commons/thumb/1/19/Mars_Climate_Orbiter_2.jpg/290px-Mars_Climate_Orbiter_2.jpg

Distance

The (average) radius of the Earth is 6371km.Calculate the Earths quadrant (1/4 of the circumference).This is not coincidence.Officially, it used to be one ten-millionth of the distance from the Equator to the north pole through Paris.Nowadays it is defined in terms of the speed of light.

Time

Calculate the time period of a pendulum whose length is one metre, using the formula where g = 9.8.

Mass

A kilogram is officially defined as the mass of a piece of platinum-iridium alloy at the Bureau international des poids et mesures, in Sevres, France.

http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/CGKilogram.jpg/800px-CGKilogram.jpg

Derived Quantities

Most quantities other than mass, length and time are derived from these quantities. For example:

Density of a Microscope Slide

Calculate the density of a microscope slide, in kg / m3.

Bookwork

Questions on page 11, 13 and 16.

Precision and Accuracy

Precision is how small the units on a measuring device are. For example, an electronic balance (scales) can measure to 0.001g, whereas kitchen scales may only measure to the nearest gram. So electronic balances are more precise.

Accuracy is how correctly something can take a measurement.

Bathroom scales may measure to 0.1g (precision) but may not do so accurately. If one scale reads a 60kg object as 59.1g, they have a precision of 0.1g and an accuracy of 1.

It's important to know how accurate a measurement in Physics is.

Assessment

A (Knowledge and Understanding)
1. Arriving Safely test (before October Break)
2. Light and Sight test (when?)

B, C (Experiment)
Do heavier objects fall faster than lighter objects? Investigation and Explanation.

D - ROTIOS (formerly One world)
1. The safety of helmets:
- are they effective?
- are they worthwhile?
- are standards high enough?
- should they be compulsory?
It may be presented as an essay, presentation or movie. It should be persuasive.
OR: The Shinkansen: history, how it works, safety, popularity, environmental issues (environmental issues and benefits over aeroplanes), and possible future developments including the new maglev train from Tokyo Osaka. You could also discuss whether or not it is likely that trains will replace aeroplanes for long-distance travel; the Seikan tunnel.

Motion

Motion means movement.

In this unit we will look at speed, acceleration and forces.

Speed (review from Grade 8)

Speed measures how fast
something's position changes with time.

Example: Melanie runs 100m
in twelve seconds. How fast
does she run in m/s?

How long will it take her to run to Yokohama station (5 km)?

x

X

Quantity (symbol)SI Unit (symbol)Other units (symbols)

Distance (d)metresKilometres (km)miles

Time (t)secondMinutes, hours (hr), days

Speed (v)metres per secondKilometres per hour (km/hr)

v

d

t

Problems

A. Kosuke is walking home. If he walks 100m in 40s, what is his average speed?
B. How long will it take him to walk to Motomachi station if it is 500m away?

Aska is riding to Kamakura, 25km away. If he rides at an average speed of 6m/s, how long will it take him to get there?

Converting m/s to km/hr

How do we convert m/s to km/hr and vice versa?


m/s m/hrkm/hr


m/s km/hr

1. Convert a driving speed of 100km/h to m/s.
2. Convert a sprint speed of 10m/s to km/h.

6060
OR 3600

3600

1000

6060
OR 3600

6060
OR 3600

Acceleration

Acceleration is a change in speed.

Speeding up, slowing down and changing direction are all acceleration.

Units are m/s2. Why?

Calculate the acceleration
in m/s2 of a car which takes
ten seconds to accelerate
from rest to 100km/h.

x

X

a

v

t

Acceleration Problems

Calculate the acceleration of a sprinter who takes two seconds to reach a speed of 10 m/s.

An object falling under gravity (assuming friction is negligible more on this in the first assignment) accelerates at a speed of 10 m/s2.How long will a falling object take to travel at 100km/hr.

How fast will a falling object be traveling after 20 seconds?

Acceleration

Calculate the acceleration of an object which takes 8 seconds to reach a speed of 24m/s.

How long will it take to reach the speed of sound, of around 340m/s?

The Human Body

Is the human body a speedometer, or an accelerometer?

http://www.vernier.com/images/cache/product.acc-bta._physics._hero._001.590.332.jpg

http://img.dxcdn.com/productimages/sku_2682_1.jpg

Images of speedometer and accelerometer unnecessary.

The Aeroplane

http://worldairlinenews.files.wordpress.com/2009/09/jal-japan-airlines-777-300-ja742j-02tko-pae-ndlr.jpg

http://www.boeing.com/news/releases/2006/photorelease/q4/061116c_lg.jpg

http://vintage.johnnyjet.com/images/PicForNewsletterJapan2005JAL747InAir.jpg

Images of aeroplanes were to show that we feel acceleration as a plane takes off and when it decelerates immediately after landing, but we don't 'feel' the speed as a plane cruises at the same speed.

Force Diagrams

An unbalanced force is required for an object to accelerate.

Falling Objects

It used to believed that heavy objects fall faster than light objects. Galileo is the first person in recorded, western history to actually test this.

Conclusion: They fell at (about) the same speed.

http://physics-animations.com/Physics/anipisa.gif

Animated GIF of Galileo not necessary.

Galileo's Philosophy

Galileo believed that theories should be simple and harmonise each other. His theory of falling objects simplified theories of motion.

He also believed that experiments were necessary to test theories, but it didn't matter if the results weren't perfect.

http://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/Justus_Sustermans_-_Portrait_of_Galileo_Galilei,_1636.jpg/220px-Justus_Sustermans_-_Portrait_of_Galileo_Galilei,_1636.jpg

Ptolemy Verses Copernicus

Ptolemy was a Greek Astronomer who devised a system of the Solar System which we now know is wrong, but which could predict the location of the planets more accurately than Copernicus's system could.

Galileo said this didn't matter, because the Copernican system was simpler and harmonised his theory about Jupiter and its moons he had discovered. Did it matter?

http://www.ps-19.org/Crea00Intro-Ps19/Astronomy_files/PtolemyEpicycles.jpg

http://www.conservapedia.com/images/thumb/0/0e/Copernicus_system.gif/300px-Copernicus_system.gif

Please load the images below.

Copernicus Verses Ptolemy

Copernicus was wrong because the planets move in Ellipses, which was later determined by the genius (arguably one of astronomy's greatest scientists) Johannes Kepler.

http://www.ps-19.org/Crea00Intro-Ps19/Astronomy_files/PtolemyEpicycles.jpg

http://www.conservapedia.com/images/thumb/0/0e/Copernicus_system.gif/300px-Copernicus_system.gif

The Hammer and the Feather

http://www.youtube.com/watch?v=5C5_dOEyAfk

What about on Earth?

If two objects of the same dimensions, surface and surface area, but different mass, are dropped, will they reach the ground at the same time? Plan and carry out an investigation to find out.

Your experiment should include a prediction, procedure, results and processing (?) and a conclusion which answers your prediction and discusses your results using a Grade 9 (or beyond) understanding of forces.

Inertia

Inertia is the property of matter which makes it resist change in its motion (acceleration).

Objects with greater mass have greater inertia. Inertia is a property of all matter, and since it increases with mass we use mass to calculate acceleration in calculations.

Inertia can be imagined by having to whirl something around in space.

http://1.bp.blogspot.com/-4G-w9-k42Fw/T3-sHh5O1qI/AAAAAAAARLM/ohv-GRyyGOo/s1600/teeth_pull_train_01.jpg

Image of a man pulling a train by attaching s wire to his teeth.

Force and Acceleration

An unbalanced force causes something to accelerate.

Newton's second law:
Force = mass * acceleration
The force is the net (combined) force of all forces acting on the object.

Example 1: A. Calculate the acceleration of a 5kg object if a force of 40N force pushes it but a friction force of 5N opposes it.
B. How long will it take the object to reach a speed of 35 m/s?

Example 2: Calculate the force required to make an 800kg car accelerate from 0 to 100km/h in one minute.
Hint: first convert everything to SI units. Second calculate the acceleration. Third calculate the force.

At the lights

Why does a motorbike accelerate faster than a car, even though it has a smaller engine (which can provide less force)?

http://howwasyourtrip.files.wordpress.com/2010/01/dsc_2881.jpg

Picture of motorcycles and a car taking off at an intersection in Vietnam removed and unecessary.

Falling Under Gravity

The Weight force due to gravity is:
Weight = mass * gravity
where g is acceleration due to gravity = 10m/s2.
(formula from MS Science)

Complete the table to show acceleration of different objects under gravity.

Mass (kg)Weight
(mass * gravity)Acceleration (force/mass)

1kg5kg10kg100kg

Quick Questions

Please answer these in your books.

1. Explain the difference and relationships between
-mass and weight
-mass and inertia

2. Explain why, in Galileo's famous experiment, the two rocks fell at the same speed, even though the one with greater mass had a stronger weight force pulling it down to Earth.

http://physics-animations.com/Physics/anipisa.gif

Friction and Drag

Drag is a type of friction which acts on an object moving through a fluid (eg the atmosphere).

What factors might affect the drag force on something?

Answer: surface, surface area, speed

Images of a baseball and a parachutist falling through the sky removed.

The Falling Ping Pong Balls

Let's oversimplify our ping pong balls to give them nice round numbers. We will assume they have just been dropped, so their speeds are similar, therefore the friction is similar.

For each, calculate: it's weight, its net force and its acceleration.

Extension exercise:
1. Sketch a graph of speed verses time and calculate how long each should take to reach the ground.
2. Two objects, of mass M and m, are dropped. Both experience the same friction force F. Calculate the acceleration of each in terms of M, m, g and F.

1kg200g

Weight = ______N

Weight = ______N

Drag = 1N

Drag = 1N

Why did Galileo's Experiment Seem to Work?

For dense objects like rocks, the friction force is much smaller than the gravitational force.

Heavier objects are generally larger (assuming the same ________), therefore they are also subjected to greater friction force.

Terminal Velocity

As a falling object's speed increases, the friction force increases but the weight force stays the same.

Eventually these two forces cancel each other out, so the speed stays the same.

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

A falling coin can be very dangerous because its surface area is very small and it is very dense, so its terminal velocity is huge.

Image of a skydiver removed.

Blog Time!

Explain the experiment we did, what we observed and why.

Did you prove Galileo wrong? Would he care? Explain your answer in as much detail as possible.

Terminal Velocity Investigation

Investigate a factor which affects terminal velocity.

TEST

When do you 'want' the test (preferably sometime next week).?

Vectors and Scalars

A scalar is a quantity with a magnitude (size) but no direction.
Eg __________________________________

A vector is a quantity for which magnitude and direction are important.
Eg __________________________________

Vectors can have a negative value. For example, if a 10N force upwards is 10N, then the same force downwards must be written (as a vector) as -10N.

When using vectors, it is important to decide which direction is positive and negative (eg North = positive, south = negative OR up = positive, down = negative

Speed and Velocity

Speed is a scalar. It does not take into account direction. A speedometer reads speed.

Velocity is a vector. Its direction is important.
Eg if a car is travelling north and has a velocity of 27m/s, what is the velocity of a car it passes at the same speed travelling south?

Displacement and Distance

Distance measures how far something has travelled. An odometer measures distance.

Displacement measures how far something is from its starting point. A GPS unit measures displacement.

http://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Odometer2.jpg/120px-Odometer2.jpg

http://fs01.androidpit.info/trss/x94/392294.png

Motion Graphs

A stone is thrown upwards at 10m/s (ignore drag). Gravity causes it to accelerate downwards at 10m/s2. Eventually it falls back down and lands at the same spot.
a) How long will it take to come to a momentary stop.
b) How long will it take to fall back down.
c) Sketch distance-time, displacement time, speed-time and velocity-time graphs for its entire path.

Time (s)

Time (s)

Speed (m/s)

Velocity (m/s)

Speed (m/s)

Velocity (m/s)

12

12

10

10

10

-10

Time (s)

Distance (m)

Displacement (m)

12

12

10

10

10

5

5

Newton's Second Law

Force = Mass * Acceleration

Newton's Third Law

Every force has an equal and opposite force.

Collisions

Collisions are important in Physics and (unfortunately) in real life for some professions, eg road safety, and (fortunately) particle physics.

A 1000kg car travelling at 100 km/hr crosses the centre-line and collides with a 10 000kg truck moving at 30km/hr in the opposite direction. After the collision, both move together. What is the final speed and direction of the combined wreckage?

What would we need to know to solve this problem, and how could we work it out?

A new quantity

Momentum, p, measures 'quantity of motion'. Heavy objects and fast-moving objects have greater momentum.

Momentum = mass * veocity.p=mv

1. What are its base units?

2. Calculate the momentum of a 1200kg car moving at 50km/hr.

Momentum is a Vector

Momentum = mass * velocityp=mv

Use units to show that momentum is the product of force and time required to push something there.

Eg Aska is riding his bike (combined mass rounded up to 100kg) and accelerates from rest to 10m/s in five seconds.
a) calculate his acceleration
b) calculate the force he provides
c) calculate the product of force and time.
d) calculate his momentum using p=mv.

Conservation of Momentum

In collisions, total momentum is always the same. In Physics terms, we say momentum is conserved.

Eg a 500 gram trolley is moving at 2 m/s, when a 100 gram block is dropped onto it. Calculate the new velocity of the trolley.

The Original Problem

A 1000kg car travelling at 100 km/hr north crosses the centre-line and collides with a 10 000kg truck moving at 30km/hr south. After the collision, both move together. What is the final speed and direction of the wreckages?

ANS: 18km/h south.

Car and a Train

A 1000kg car stops on a railway line, and a 5000 kg train traveling at 60km/h North collides with it. After the collision, both the car and the train stick together. Calculate the velocity of the train and the car after the collision.

ANS: 16.340m/s North

Momentum and Time

For something to change momentum quickly, it must have a large force exerted on it. This force can be fatal in collision.




Eg. A car is travelling at 20m/s when it crashes into a tree. It takes a 50kg person in it 0.2s to stop when they hit the windscreen. Calculate the average force on the person.

It's All About the Time

Time is critical in determining the force on something which changes momentum suddenly.

What can be done to increase the time it takes something to stop?

http://www.carlsbadchiropractic.com/airbag.jpg

Safety

Explain how airbags reduce harm during accidents.

Explain how helmets reduce harm during accidents.

Outline three reasons for and against helmets being compulsory.

Formative assessment: How do you want to present it?

Extension: The pool table
(2 Dimensions)

What's the danger?

What can we do about it?