When most people are asked what makes rockets lift off they say it's caused by the push of the exploding fuel against the ground. Explain why this is wrong.
For every action, there is an equal and opposite reaction. That's from Newton, I think, but it may have been from one of those other clever guys in physics. The push is out the back. The rocket moves to the front.
The misconception that rockets lift off due to the push of the exploding fuel against the ground stems from an incomplete understanding of Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. While it is true that the exhaust gases expelled from the rocket engine create a force pushing backward, it is important to understand that this force is not directly responsible for lifting the rocket off the ground.
To understand how rockets actually lift off, we need to examine the concept of conservation of momentum. In a rocket, the expulsion of exhaust gases generates a force in one direction, which leads to an equal and opposite force that propels the rocket forward. According to Newton's third law, the rocket exerts a force on the gases, causing them to accelerate backward, while simultaneously experiencing an equal and opposite force that propels the rocket forward.
This principle can be illustrated using the example of a person standing on a skateboard. If the person forcefully throws a heavy object in one direction, they will experience an equal and opposite force causing them to move in the opposite direction. Similarly, the rocket experiences a propulsion force in the forward direction due to the expulsion of gases.
To achieve liftoff, the generated forward propulsion force must be greater than the force of gravity pulling the rocket downward. This is achieved by the rocket's engines continuously expelling high-speed exhaust gases, which create a thrust force that propels the rocket upward. The reaction force from the expelled gases is not directly pushing against the ground, but it is pushing against the rocket itself, propelling it forward and upward.
Therefore, the misconception that the push of the exploding fuel against the ground directly causes rockets to lift off is incorrect. The lifting force is a result of the expulsion of gases creating a forward propulsion force, which overcomes the force of gravity and enables the rocket to ascend into space.