CITY SCIENCE STARS: Kick-off to Lift-off

SHOOT FOR THE MOON! What forces are involved here? Think about forces on the individuals and also consider the forces on a ball when it is kicked. A common misconception is that the ‘kick’ on a ball is a force that remains on the ball until it stops moving. The force of the kick only exists when it is imparted on the ball. The ball will continue to accelerate in the direction of the force until opposing forces (air resistance and ground friction) balance the force or are greater and slow the ball down to an eventual stop. Gravity is pulling the ball downwards at all times (so it will fall down through the air or remain on the ground). If forces on an object are balanced, a stationary object will remain still and a moving object will continue to travel at a constant speed. If forces on an object are unbalanced, a stationary object will start to move and a moving object will speed up, slow down or change its direction. Forces may cause an object to change shape. For every action (force), there is an equal and opposite reaction (force). So when you kick a ball, your foot experiences an equal force from the ball.

Isaac Newton’s Laws of Motion HOW DO ROCKETS WORK? LIFT DRAG THRUST The greatest amount of thrust is needed to launch the rocket (as it is at its heaviest, with the greatest fuel load on board), overcome gravity and air resistance. Once the rocket escapes the Earth’s atmosphere there is little drag, so very little thrust is needed to propel the rocket forward. GRAVITY Isaac Newton’s Laws of Motion Published in 1687

WHERE DID ROCKETS COME FROM? China Year ~1200 Germany WW2 Global Modern era

BUILD YOUR OWN PAPER ROCKET! Body tube (room for engine, fuel and cargo) Nose cone Mission logo Exhaust nozzle (hole for launcher) The paper ‘rockets’ are not really rockets, because like a football, they are being pushed away by an applied force (from the air forces out of the bottle when it is stomped). We are creating a ‘projectile’ where the force pushes in the same direction as the motion. More able children should be able to distinguish between these situations. Actual rockets rely on thrust: the force of burning gases expelled out of the rear of the rocket create an equal and opposite force on the rocket, which propels it forward. Fins

EXPERIMENTAL DESIGN To design a fair rest, each team should pick one factor to vary and keep the rest the same Length of rocket Weight of rocket Number of fins Size or shape of fins Shape of nose cone …something else? HOWEVER, if the challenge is to be to come up with the best design, it is perfectly acceptable to change multiple variables (and not carry out a fair test) and simply compare the overall designs for their effectiveness.

EXPERIMENTAL DESIGN 1 - Low launch trajectory (pass) 2 - Medium launch trajectory (shot) 3 - High launch trajectory (lob)

Let’s go launch some rockets! ROCKET LAUNCH EXPERIMENT Let’s go launch some rockets!

ROCKET LAUNCH EXPERIMENT Which angle sent the rockets the furthest? Which design sent the rockets the furthest? What could we do to improve our designs? How might real rockets generate thrust?

FIZZ, BANG, ZOOM! – ROCKET CHEMISTRY Stomp-rockets get their driving force from air in the launchers pushing them forward, but where does the thrust for full-size rockets come from? Chemical rocket engines rely on the combustion (burning) of fuel to create exhaust gases that fire out of the bottom! Courtesy of NASA A driving force is one where the force (push) is in the same direction as the travel (e.g. air pushing the paper rocket). Thrust is generated when a force generated in one direction causes a force and movement in the opposite direction (e.g. burning fuel pushing out of rear of rocket forces rocket itself to move upwards) The tablets are dissolved in the water, which allows chemicals in the tablet (usually citric acid and bicarbonate of soda) to react and create carbon dioxide gas (amongst other things) The gas builds up and is then forced out This is the principal of how real rockets work, but on a massive scale and with much more powerful fuels that rely on a burning reaction Isaac Newton’s 3rd law of motion – for every action, there is an equal and opposite reaction. chemical rocket engines. Chemical rocket engines use the combustion of propellants to produce exhaust gases as the working fluid. The high pressures and temperatures of combustion are used to accelerate the exhaust gases through a rocket nozzle to produce thrust. There are two important parts of a chemical rocket engine; the nozzle, and the propellants. The nozzle design determines the mass flow rate, exhaust velocity, and exit pressure for a given initial pressure and temperature. The initial pressure and temperature are determined by the chemical properties of the propellants. Propellants are composed of a fuel to be burned and an oxidizer, or source of oxygen, for combustion. Under normal temperature conditions, propellants do not burn, but require some source of heat, or igniter, to initiate combustion. Chemical rocket engines do not typically rely on the surrounding atmosphere as a source of oxygen. Therefore, chemical rocket engines can be used in space, where there is no atmosphere present.

WHAT HAVE WE LEARNED TODAY? The forces involved in kick-offs and lift-offs How to build and launch paper rockets How design and angle affects performance How chemistry makes rockets go with a bang!

Primary Science Specialist sarah.eames@pstt.org.uk Alex Evans LCFC STEM Coach alex.evans@lcfc.co.uk Sarah Eames Primary Science Specialist sarah.eames@pstt.org.uk