AP Physics questions on Weightlessness in Orbit

📚 Quick Study Guide

• ⚖️ Weightlessness doesn't mean zero gravity; it means the absence of perceived weight due to freefall.
• 🛰️ In orbit, objects are constantly falling towards Earth, but their tangential velocity keeps them moving around the planet.
• Newton's Law of Universal Gravitation: $F = G \frac{m_1m_2}{r^2}$, where $F$ is the gravitational force, $G$ is the gravitational constant, $m_1$ and $m_2$ are the masses, and $r$ is the distance between their centers.
• 🚀 Orbital velocity ($v$) can be calculated using: $v = \sqrt{\frac{GM}{r}}$, where $G$ is the gravitational constant, $M$ is the mass of the central body (e.g., Earth), and $r$ is the orbital radius.
• 🌍 Apparent weight ($W$) is the normal force exerted on an object. In orbit, $W=0$ because the object and its surroundings are in freefall.
• 🤔 Weightlessness is experienced when the gravitational force is the only force acting on an object.

🧪 Practice Quiz

1. A spacecraft is orbiting Earth. Which statement is most accurate regarding the astronauts inside?
   1. They are weightless because there is no gravity in space.
   2. They are weightless because they are in freefall.
   3. They have the same weight as they do on Earth.
   4. They have less weight than they do on Earth, but not zero.
2. What is the primary reason astronauts experience weightlessness in orbit?
   1. The absence of air resistance.
   2. The spacecraft is moving at a constant speed.
   3. The balance between gravitational force and the centripetal force needed for orbit.
   4. The low density of objects in space.
3. If a satellite is orbiting Earth at a constant altitude, what force is primarily responsible for keeping it in orbit?
   1. Friction from the atmosphere.
   2. The normal force from the Earth's surface.
   3. The Earth's gravitational force.
   4. The satellite's propulsion system.
4. An astronaut inside the International Space Station (ISS) appears to float. This is because:
   1. The astronaut is beyond the reach of Earth's gravity.
   2. The astronaut and the ISS are both accelerating towards Earth at the same rate.
   3. The astronaut has no mass in space.
   4. The astronaut is pushed away from the Earth by the solar wind.
5. Two satellites of equal mass are orbiting Earth. Satellite A is in a lower orbit than Satellite B. Which satellite has a higher orbital velocity?
   1. Satellite A
   2. Satellite B
   3. Both have the same orbital velocity.
   4. The answer cannot be determined without knowing the exact altitudes.
6. What happens to the perceived weight of an object in a freely falling elevator?
   1. It increases.
   2. It decreases, but doesn't reach zero.
   3. It becomes zero.
   4. It remains the same.
7. A person is standing on a scale inside a spacecraft orbiting Earth. The scale reads zero. This indicates:
   1. The spacecraft is beyond Earth's gravitational field.
   2. The person has lost all their mass.
   3. The person and the spacecraft are in freefall.
   4. The scale is broken.