Year 10 Physics

Why Study Physics? By studying Physics it does not necessarily mean you are

setting out to explicitly be a physicist…

Okay, so you may want to do exactly this, and that’s cool

…BUT Physics is a subject that equips you with skills which open up a huge range of future opportunities.

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Here are a few jobs that involve Physics?

Acoustics, Aeronautical Engineer, Agricultural Engineer, Air Traffic Controller, Airline

Pilot, Archaeologist, Architect, Astronomer, Audio Engineer, Broadcasting, Cartographer, Chartered Surveyor, Civil Engineer, Climatologist, Clinical Scientist, Computing, Designer, Doctor, Electrical Engineer, Energy, Engineering, Environment, Environmental Scientist, Forensic Scientist, Gas Engineer, Geologist, Geophysicist, Health Services, Journalist, Laboratory Technician, Marine Engineering, Mathematician, Mechanical Engineer, Medical Physicist, Meteorologist, Naval Architect, Naval Career, Nuclear Scientist, Oceanographer, Operational Research, Patent Agent, Patent Examiner, Pharmacist, Photonics, Radiation Protection, Radiographer, Scientific Officer, Space and Remote Sensing, Teacher, Transport, Water Management…

The list goes on and on!

Physics training can be an asset in ANY job that involves problem solving, communication, investigative skills, analytical skills, attention to detail, ethical behaviour, practical skills and lab safety, critical thinking, logical processing, etc, etc…

But what is Physics really about? What the curriculum says… At Years 9 and 10:

The explanation of the motion of objects involves the interaction of forces and the exchange of energy and can be described and predicted using the laws of physics.

Motion is a change in position of an object with respect to time.

A force is any interaction that can change the motion of an object.

Energy is never created or destroyed, it is only changed from one state to another.

LETS MAKE THIS REAL…

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The indisputable relevance of Physics to real life is something which many people, adults and kids alike, are not intrinsically aware of.

How do planes fly?

Why is the sky blue?

What happens when I plug my phone charger into a plug socket?

Why do sports shoes have soft inserts?

Crumple zones, they just don’t make cars like they used to!

When someone makes a race-car noise, why do they change the pitch of their VROOOMMM…?

Why does a balloon stick to a wall after I rub it on my hair?

Rainbows, sun halos, phases of the Moon?

All of this is Physics…

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You probably already know much more about Physics (specifically forces, energy and motion) that you realise.

To help you get started have a look at the pictures below and think about the forces acting on the body in each case.

Year 10 Physics

Scalars & Vectors

In Physics lots of measurements are made.

Each of these quantities can be defined as a scalar or a vector.

A scalar is a measurement that has only a magnitude (or size).

A vector is a measurement that has both magnitude and direction.

From the following list identify the scaler terms and the vector terms and organise them in to a table.

Speed Distance Time Velocity Displacement Acceleration Mass Force Weight Energy Power Work Temperature

Speed or Velocity? Speed = distance ÷ time Velocity = displacement ÷ time

The units for both speed and velocity are metres per second

ms-1 where distance is measure in metres (m), and time in seconds (s).

Speed or Velocity? We use km/hr far more frequently in everyday situations

however than ms-1.

The conversion is easy, but very important!

Try converting 100 km/hr to ms-1 first using the short hand method shown, and then step by step. How many metres per minute is 100 km/hr?

A useful short hand method is the 3.6 conversion: • ms-1 to km/hr = multiply by 3.6 • km/hr to ms-1 = divide by 3.6

Speed or Velocity Speed is therefore a scalar quantity, as it only has magnitude.

For example you might say a car is travelling at 100 km/hr on the freeway, the direction does not matter.

Velocity however had both magnitude and direction. You must state which direction the object is travelling. For example a car traveling at 100 km/hr on the Stuart Highway

from Alice Springs to Darwin, is travelling at 100 km/hr in a northerly direction.

Directions are typically given as up/down, left/right or compass bearing (degrees from north).

Questions

a) In 2009, Jamaican sprinter Usain Bolt ran the 100-metres in a record time of 9.58 seconds. What was his average speed? Give your answer both in ms-1 and km/hr.

b) In 2.5 seconds a skydiver in free fall drops a distance of 150 metres. What is their velocity? Give your answer both in ms-1 and km/hr.

c) It takes your teacher 35 seconds to walk around the classroom and back to the front desk. What was their average velocity? Give your answer both in ms-1 and km/hr.

Long Question An aircraft takes off and flies east for 30 min with a ground speed of

200km/hr. It then flies north a distance of 120 km, with a tailwind it had a ground speed of 240 km/hr. It then flies back to its starting point with a speed of 180 km/hr.

Use this information to find:

a) The distance travelled in the first leg b) The time taken to fly the second leg c) The distance and the time taken to fly the final leg d) The velocity of the final leg e) The planes average velocity over the whole flight

TIP: Draw the situation first. REMEMBER: a2 + b2 = c2 and SOH CAH TOA

Speed and Velocity Demo

Okay, so no matter how hard you try, you can’t make a paper plane fly as fast as in the previous question.

But how fast can you make a paper plane fly?

Think what designs will go fastest? Less drag is a good starting point.

How will you determine the average speed of the plane you make?

Paper Plane See supplementary worksheet for detailed

instructions on making the paper plane shown below.

Or you can design your own!

Whatever design you choose, the nose of the plane is sharp, DO NOT throw at other people!

Acceleration

Acceleration tells you how quickly the velocity of a moving object changes.

Recall that v = d/t, where velocity is measured in metres per second (ms-1).

By definition, the average acceleration of an object can be calculated by dividing the change in velocity by the time taken for the change to occur:

The triangle-shaped symbol is used to represent the change in a value; this symbol (taken from the Greek alphabet) is called delta.

Units of Acceleration The units of acceleration are metres per second

per second, or metres per second squared.

We write this as m/s2 or ms-2

If we look at how acceleration is calculated, it is

easy to see where these units come from: Velocity is measured in m/s Time is measured in s Acceleration is velocity divided by time,

therefore m/s ÷ s

In words that is metres per second per second!

Earths gravity causes falling

objects to accelerate at

~ 9.8 ms-1.

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QUESTIONS

a) A downhill skier travelling at 20 ms-1 slows down at the end of a run, coming to a complete stop in a distance of 10 m. What was her average acceleration?

b) An aircraft commences a rolling start on the runway, moving initially at 10 km/hr the pilot applies full throttle, after 12 seconds she takes-off at a velocity of 140 km/hr. What was her acceleration down the runway?

When you speed-up acceleration is positive. When you slow down your acceleration is negative (deceleration).

Acceleration, like velocity is also a vector quantity.

Graphing straight-line motion Distance-time graph

The distance from a certain point is given on the vertical axis and time on the horizontal axis.

The velocity can be calculated by finding the gradient of the graph.

Gradient = rise/run Velocity = distance/time

Graphing straight-line motion Velocity-time graph

velocity or speed of an object on the vertical axis and time on the horizontal axis.

The distance travelled can be calculated by finding the area under a velocity-time graph.

Acceleration is the gradient of a velocity-time graph.

Gradient = rise/run Acceleration = Δvelocity/time

Area under graph = x-axis x y-axis

Distance travelled = velocity x time

Acceleration due to Gravity Because we know that falling objects accelerate at 9.8 ms-1 at the

Earths surface, we can use this to determine how fast a falling object hits the ground!

TRY IT! Get a tennis ball or similar, and drop it from rest. Using the slow

motion camera feature on your phone/tablet/computer accurately record how long it takes to fall.

You know that a = 9.8 ms-1, as its gravity, the initial velocity was zero,

and you have just recorded the time. Rearrange the formula: Δv = a × t and substitute in the values…

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So far when we have talked about objects speeding up and slowing down, we have talked about them as isolated systems.

In practice, an object must have an external force acting on it for acceleration to occur. An engine perhaps A person pushing a pram Gravity

In other words, there must be a none zero net force for an object to undergo acceleration/deceleration.

If the force is continually applied, the object will continue to accelerate. THINK – What limits apply to this?

Acceleration in Sport Acceleration is more important than top speed/velocity in many sports.

Think about it, aside from specific running events, in most

sports the athlete does not run more than a few tens of metres in any one direction before stopping or turning.

A high top speed is good, but the ability to achieve maximum velocity within the shortest time frame is more important than the maximum speed itself.

Many athletes never actually reach their top speed during a competition.

Wrapping it up… Just how fast can your legs accelerate you?

Does being the fastest runner on the team mean you can also accelerate the fastest?

How could you test this?

TASK: To design a fair and repeatable experiment that answers the above question. Maybe you skate or ice dance? Perhaps you could try the same on 8 wheels or blades…

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ts Developed by Sci-Fly STEM Outreach, in conjunction with The Growing

Tall Poppies Science Partnership Program, 2017.

These resources are provided for educational use across Australia and beyond. Content is curriculum matched to the Australian Year 10 Physical Sciences.

Several years of in school experience has been combined to produce the content. From profession reading and curriculum development to informal discussions and impromptu learning moments.

We thus acknowledge everyone who may have contributed to this pool of knowledge.

If for any reason you feel any content has been used unfairly please let us know and we will either immediately remove it, or add the correct acknowledgment upon notification.

All images have been produced especially for this project by artist Saran Kim. They can be freely reproduced for educationally purposes only, where due credit to the original source is provided.