Education
Air Rocket
What happens?
You place an empty (except for air) 500 millilitre water bottle on the nozzle of a pump. The door of the bottle chamber is closed carefully to create a seal. You then operate a pump until the red light flashes to indicate the bottle can be launched. The bottle shoots up through an arched channel to land in a basket some metres away.
How does it work?
As air is pumped into the bottle, the air pressure inside the bottle increases. The increasing resistance of this air makes it harder and harder to push the plunger down. When the bottle is closed the pressures inside are equal in all directions, there is no resultant force or acceleration and the bottle remains stationary. When the bottle is opened, there is no longer a force on its open end: the remaining pressure gives a resultant upward force on the closed end, accelerating the bottle upwards. The compressed air expands out of the bottle until the air density inside the bottle is equal to that of the surrounding air, and there is no further acceleration. The bottle reaches its highest point, and then falls.
In energy terms, you put energy into the system as you operate the pump: chemical energy from your body is converted to elastic potential energy in the compressed air. This elastic energy is then converted to the kinetic energy of the bottle on its release (plus some sound and heat energy). This kinetic energy is converted to gravitational potential energy as the bottle rises, and back to kinetic energy as it falls, and sound and heat energy as it hits the basket.
Why is it important?
There is a wide range of aircraft: balloons, airships, propeller and jet driven aeroplanes, and space rockets, for example. Aeroplanes are the most effective means of air travel near the Earth's surface. However, as their operation depends on using lift from the air to keep them up, and oxygen from the air to support fuel combustion, they cannot be used space travel, as there is no air in space. For this, some form of propulsion independent of air is necessary. Compressed gas is a possibility, as in this exhibit, but its use is limited by the small amount of elastic energy it can safely store. Most rockets now use chemicals, like oxygen and hydrogen, which when mixed, combine in an exothermic (giving out heat energy) reaction to produce gas which is expelled from the rear of the rocket. This results in the rocket's forward propulsion.
How does it relate to the primary curriculum?
- Curriculum objectives: Mutual understanding (if working in a pair or small group)
- Cross-curricular skills: Communication (if working in a pair or small group)
- Thinking skills and personal capabilities: Thinking, problem solving, decision making; Working with others (if working in a pair or small group)
- Area of learning - The world around us: Pupils can explore: how they and others interact in the world; the causes and effects of movement, forces and energy
- Learning experiences: Investigating and problem solving; Active and hands on
- Attitudes and dispositions: Curiosity
How does it relate to the post-primary curriculum?
- Science: Pupils should have opportunities to explore the effects of energy transfer
Thinking skills
Perceiving and establishing relationships between consequences and their causes; Drawing conclusions, or relating conclusions and reasons
Learning styles
Visual; Kinaesthetic
Where can you find out more?
www.howstuffworks.com/rocket.htm (how rockets work)