Rockets

Rocket  A chamber enclosing a gas under pressure  Small opening allows gas to escape providing thrust in the process  Which of Newton’s Laws?  Gas is produced by burning propellants  Solid  liquid

Newton’s First Law  Object in motion/rest will stay in motion/rest until acted upon by an unbalanced force.  Rocket at rest on launch pad  Thrust from engines against pad push rocket up as gravity tries to pull it down.  When rocket runs out of fuel, gravity pulls rocket back  In orbit a space craft will travel in a straight line until it is acted upon by a gravitational pull  Path becomes and arc, path will match the shape of the body it is traveling around (this is called an orbit )  Unless slowed down by another force the craft will orbit the body forever  What forces could slow or stop the craft?

Newton’s First Law  If an object, such as a rocket, is at rest, it takes an unbalanced force to make it move. If the object is already moving, it take an unbalanced force to stop it, change its direction from a straight line path or alter its speed

Newton’s Third Law  Every action has an opposite and equal reaction  Rocket can only thrust when it expels gas out of the engine  Rocket pushes on the gas and the gas in turn pushes on the rocket  Think of riding a skateboard and jumping off that skateboard  Rider move in direction of jump  Board moves in opposite direction, farther than rider move forward  Unequal distance happens because of the difference of mass

Newton’s Third Law  In order for the rocket to lift off the launch pad, the action or thrust from the engine must be greater than the weight of the rocket.  Rockets work better in space because there is less air friction (drag) than in Earth’s atmosphere. The exhaust gas can escape the engine freely

Newton’s Second Law  Force = mass X acceleration or F=ma  Explained: lets use the skate board example The rider jump off the board. The force acting the on the rider is equal to the force acting on the board. So the equation looks like this: Mass(rider) x acceleration(rider) = Mass(board) X acceleration(board) Both sides of the equation have to be equal. Since the rider has more mass than the board the rider’s acceleration has to be less than the acceleration of the board

Newton’s Second Law  Thrust for a rocket continues as long as there is fuel to burn.  As long as fuel is burning the rockets mass is changing. A majority of the rockets mass is propellant, as it burn the rocket’s mass decreases  The rocket’s acceleration will increase as its mass decreases.  This is a major reason why a rocket starts slow and speeds up.  Rocket must achieve a speed of 40,250 kmh to escape Earth’s gravitational pull. This is called escape velocity  The greater the mass of rocket fuel burned, and the faster the gas produced can escape the engine, the greater the thrust of the rocket

Putting it together  An unbalanced force must be exerted for a rocket to lift off from a launch pad or for a craft in space to change speed or direction (First Law).  The amount of thrust (force) produced by a rocket engine will be determined by the rate at which the mass of the rocket fuel burns and the speed of the gas escaping the rocket (Second Law).  The reaction, or motion, of the rocket is equal to an in the opposite direction of the action, or thrust, from the engine (Third Law).