arriving safely
Post on 16-Apr-2017
2.899 Views
Preview:
TRANSCRIPT
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?
top related