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?
Mathematics● “The Book of Nature is Written in the Language of Mathematics.” -Galileo Galilei (image from Wikipedia)
Scientific NotationScientists often use scientific notation / standard form. How comfortable are you with this. Example Problems 1. Write ten million in scientific notation. 12 2. Write 4.3 * 10 as an ordinary number. 3. What is 4*1012 / 2*109?
More Metric Conversions10-2 mental1012 bulls10-12 boos10 millipedes106 aches
le Système international dunités (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 haven’t 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/co Mars_Climate_Orbiter_2.jpg
DistanceThe (average) radius of the Earth is 6371km.Calculate the Earth’s 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 thespeed of light.
TimeCalculate 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. mass density= volume
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.● Its 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 distance somethings position changes with time. Speed = time Quantity SI Unit Other units (symbol) (symbol) (symbols) Distance (d) metres Kilometres (km) miles Time (t) Speed (v) second metres per Minutes, hours (hr), days Kilometres per d second hour (km/hr) ÷ ÷● Example: Melanie runs 100m in twelve seconds. How fast v X x t does she run in m/s?● How long will it take her to run to Yokohama station (5 km)?
Problems1. 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?2. 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 ×60×60 m/hr ÷1000 km/hr OR ×3600 m/s ×3600 km/hr1. Convert a driving speed of 100km/h to m/s.2. Convert a sprint speed of 10m/s to km/h.
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 v 2 of a car which takes in m/s ten seconds to accelerate ÷ ÷ from rest to 100km/h. a X x t
Acceleration Problems1)Calculate the acceleration of a sprinter who takes two seconds to reach a speed of 10 m/s.2) An object falling under gravity (assuming friction is negligible – more on this in the first assignment) accelerates at a speed of 10 m/s 2. How long will a falling object take to travel at 100km/hr.3)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? Images of speedometer and accelerometer unnecessary.http://www.vernier.com/images/cache/product.acc-bta._physics._hero._001.590.332.jpg http://img.dxcdn.com/productimages/sku_2682_1.jpg
The Aeroplane Images of aeroplanes were to show that we feel acceleration as a plane takes off and when it decelerates immediately after landing, but we dont feel the speed as a plane cruises at the same speed. http://worldairlinenews.files.wordpress.com/2009/09/jal-japan-airlines-777-300-ja742j-02tko-pae- ndlr.jpg http://vintage.johnnyjet.com/images/PicForNewsletterJapan2005JAL747InAir.jpghttp://www.boeing.com/news/releases/2006/photorelease/q4/061116c_lg.jpg
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 Animated GIF objects. Galileo is the of Galileo not first person in necessary. recorded, western history to actually test this.● Conclusion: They fell at (about) the same speed. http://physics-animations.com/Physics/anipisa.gif
Galileos 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 didnt matter if the results werent perfect. http://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/Justus_Sustermans_-_Portrait_of_Galileo_Galilei,_1636.j Justus_Sustermans_-_Portrait_of_Galileo_Galilei,_1636.jpg
Ptolemy Verses Copernicus● Ptolemy was a Greek Astronomer who devised a system of the Solar Please load the System which we now images below. know is wrong, but which could predict the location of the planets more http://www.conservapedia.com/images/thumb/0/0e/Co accurately than Copernicuss system could.● Galileo said this didnt http://www.ps-19.org/Crea00Intro-Ps19/Astronomy_file matter, because the Copernican system was simpler and harmonised his theory about Jupiter and its moons he had discovered. Did it matter?
Copernicus Verses Ptolemy http://www.conservapedia.com/images/thumb/0/0e/Copernicus_system.gif/300px-Copernic http://www.ps-19.org/Crea00Intro-Ps19/Astronomy_files/PtolemyEpicycles.jpgCopernicus was wrong because the planets move in Ellipses,which was later determined by the genius (arguably one ofastronomys greatest scientists) Johannes Kepler.
The Hammer and the Featherhttp://www.youtube.com/watch?v=5C5_dO
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 Image of change in its motion a man (acceleration). pulling a train by● Objects with greater mass attaching have greater inertia. Inertia is s wire to a property of all matter, and his teeth. since it increases with mass we use mass to calculate acceleration in calculations. http://1.bp.blogspot.com/-4G-w9-k42F● Inertia can be imagined by having to whirl something around in space.
Force and Acceleration● An unbalanced force causes something to accelerate.● Newtons 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)? Picture of motorcycles and a car taking off at an intersection in Vietnam removed and unecessary.http://howwasyourtrip.files.wordpress.com/2010/01/dsc_2881.jpg
Falling Under Gravity● The Weight force due to gravity is: Weight = mass * gravity 2 where g is acceleration due to gravity = 10m/s . (formula from MS Science)● Complete the table to show acceleration of different objects under gravity. Mass (kg) Weight Acceleration (mass * gravity) (force/mass) 1kg 5kg 10kg 100kg
Quick Questions● Please answer these in your books. 1. Explain the difference and relationships between -mass and weight -mass and inertia http://physics-animations 2. Explain why, in Galileos 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.
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● Lets 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: its 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. Drag = 1N Drag = 1N 1kg 200g Weight = ______N Weight = ______N
Why did Galileos 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 objects 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://fs01.androidpit.info/trss/x94/392294.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/Odometer2.jpg/120px-Odometer2.jpg
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.
Speed (m/s) Velocity (m/s) 10 10 1 2 Time (s) 1 2 Time (s) -10
Distance (m) Displacement (m) 10 10 5 5 1 2 Time (s) 1 2
Newtons Second Law Force = Mass * Acceleration Newtons Third LawEvery 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 quantityMomentum, 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 * velocity p=mvUse units to show that momentum is the product of force and time required to push something there. Eg Aska is riding his bike (combined massrounded 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 MomentumIn collisions, total momentum is always the same.In Physics terms, we say momentum isconserved.Eg a 500 gram trolley is moving at 2 m/s, when a100 gram block is dropped onto it. Calculate thenew velocity of the trolley.
The Original ProblemA 1000kg car travelling at 100 km/hr northcrosses the centre-line and collides with a 10000kg truck moving at 30km/hr south. After thecollision, both move together. What is the finalspeed 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 sticktogether. 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. p F= t 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.
Its 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? p F= t 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) Whats the danger? What can we do about it?
A particular slide catching your eye?
Clipping is a handy way to collect important slides you want to go back to later.