A: Slicks (i.e., no tread) but these are only good when there is no rain.

Gear Ratios:
Now that everyone has finished building their gear system, let’s talk about what a GEAR RATIO is. A good way to visualise this is by imagining you are wrapping a tape measure around each gear. If the smaller gear is half the size the larger gear, the tape measure could wrap around small gear twice as many times as it does the large gear.

An example of this can be seen below: let’s say the perimeter of the large gear is 12 cm, measured with the measuring tape. The perimeter of the small gear is 6cm, which means that if we were to wrap the 12 cm from the large gear around the small gear, it would fit around the object twice.

The gear ratio is calculated by comparing the total driving gear’s teeth to the total driven gear’s teeth. In the example above, this would be 12 to 6 which could be simplified as 2:1.

(Image source: https://commons.wikimedia.org/wiki/File:Animated_two_spur_gears_1_2.gif)

Torque

Ratios

Ratios are comparisons. The following scenario involves a ratio of 1:7.

There were 24,000 people at a concert. For every 7 adults there was 1 child. How many children were at the concert?

Power to weight ratio
The ratio between power and weight is a common consideration when dealing with the performance of an engines and motors. This principle can even be seen in humans when competing in competitions such as Ninja Warrior. The following video (3:13) discusses the power to weight ratio in terms of cycling.

Newton's three laws of motion

Newton's three laws of motion are explained in the following video (3:32). These laws were first stated by Isaac Newton in 1687. The three laws may be summarised as follows:

1. Every object in a state of uniform motion will remain in that state of motion unless an external force acts on it.  This is also know as inertia.
2. Force equals mass times acceleration (F=ma)
3. For every action there is an equal and opposite reaction.

 

Hovercrafts

Rocket sled

This interactive rocket sled simulation allows you to change certain variables in real time and see the results.

(https://www.physicsclassroom.com/Physics-Interactives/Newtons-Laws/Rocket-Sledder/Rocket-Sledder-Interactive)

Boats, submarines and buoyancy

This video shows a simple experiment investigating density and buoyancy (3:19).

Archimedes principle

This TED-Ed video (4:42) is an animated depiction of Archimedes and his pioneering work with buoyancy.

Submarines

The following video (2:33) explains how submarines work using air to change their buoyancy.

 

Velocity and acceleration

This video (2:02) explains how acceleration is the rate at which velocity changes over time. It also features some examples of how to use mathematics to calculate the average acceleration.

Skateboards, roller skates and roller blades

Conservation of energy

The law of conservation of energy states that energy can neither be created nor destroyed - only converted from one form of energy to another. The following video (1:36) demonstrates this with vivid examples of kinetic and potential energy.

Kinetic energy

Kinetic energy is the energy that an object has because of its motion. The formula for kinetic energy is:

Kinetic Energy Calculator

 

Gears and ratios

Gears are a common way to utilise mechanical advantage in transportation. What are some forms of transportation that you can think of that use gears? 

Activity:
For today’s activity, everyone is going to be divided into groups of two, and each group will receive a Lego kit. Your task is to build a gear system. Use your creativity to create something interesting! There is no one way to do it – try different options!

Differentials

This video (5:18) is more advanced than Year 4 children would normally encounter but the main points are that wheels turn at different speeds when cornering and that gears are one way to enable this. Students will also explore how wheels on a non-fixed axle such as on a pram or billy cart are free to turn at different rates.

Electric vehicles

Internal combustion engines

Motorcycles

Cars

 

Air travel

Planes, helicopters and gliders are some of the more common types of air travel. The following video (3:00) explains why the wind blows which is an important consideration for weather patterns and air travel.

Air travel and the Earth's rotation

The following video (3:15) explains the effect of the Earth's rotation on air travel.

Lift

Rockets

Space ships

Air pressure experiments

The following video (10:18) is about straws and it explains that suction is really a difference in pressure. It also makes the point that "Nothing sucks in science".

 

Relative motion

The following video (6:26) on relative motion is an important introduction to the idea that everything is in constant motion. Related terms include 'frame of reference'.

Hydraulics

Pascal's principle states that the pressure applied to any part of an enclosed liquid will be transmitted equally in all directions through the liquid. The following screenshot is from a video (3:22) about the application of Pascal's law in hydraulics. It shows the formula for comparing both sides of a hydraulic jack.

 

 

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