<p>Can someone please help me how in terms of physics the following things happen?</p>
<p>1) Why does a rocket go up?</p>
<p>You can use several different ways to understand:
-dp/dt=F and since newton 3rd law, there is an force on the rocket that accelerates the rocket
- Conservation of momentum: If rocket is an isolated system, then the momentum of the air particles that move really fast have to be counterbalanced by the momentum of the Rocket itself, moving relatively slowly
- Least rigorous way: The particles (fuel) being heated bump into the top of the rocket engine, creating a force (once again dp/dt= F, and since when they bump, their momentum change) upward. That force is NOT counterbalanced by a force downward b/c the air particles at the bottom of the rocket escape out and do not bump (because there’s a hole at the bottom of a rocket).</p>
<p>2) In newtons’s cradle what happens when a person lifts one marble and let it go? (I mean I understand that energy from the marble that is lifted gets transferred to all the other marbles inbetween cause the, marble at the other end to rise. But how does this work?)</p>
<p>Don’t understand.</p>
<p>3) Two hockey pucks are on ice. One is mass M and the other is mass m. M > m. Same force is applied to each. Same distance, A, is traveled. As m reaches A, is its speed larger or less than M.</p>
<p>The only thing that matters here is acceleration, because once you know the acceleration, computing velocity using kinematics is trivial. So the acceleration of big puck << small puck (F=ma). vf*vf=2ax, so vf proportional to a square rooted, given constant x, so speed of light puck faster. </p>
<p>I think you can use integral F.dx= KE, but that’s again another form of the kinematics that accounts for mass.</p>
<p>4) Two cars collide. What can you say about the forces each feels if one car is much heavier than the other. The speed of each car is different.</p>
<p>Newton’s third law: equal force on each other. Don’t care about speed, about mass of car.</p>
<p>5) Why do astronauts experience weightlessness? Is there really no gravity in space?</p>
<p>Because they “fall” continuously down toward the earth. The only difference is that they move sideways each time, and never actually hit the ground b/c the earth’s curvature, matches the curvature of their path (imagine shooting a bullet sideways from a high tower, so fast that it falls down, but never reach the ground because the earth “moves away” by having a curvature.</p>
<p>Hope that helps.</p>