📚 Understanding True Weight and Apparent Weight
Let's clarify the difference between true weight and apparent weight, particularly in the context of orbiting objects like satellites or astronauts on the International Space Station (ISS).
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True Weight: This is the actual force of gravity acting on an object. It's calculated using Newton's law of universal gravitation. Your true weight doesn't change unless your mass or the gravitational field strength changes.
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Apparent Weight: This is the force you *feel* as weight. It’s often the normal force exerted on you by a supporting surface. If you are in freefall, your apparent weight is zero, even though your true weight is still there. Think about it like this, if you were standing on a scale in an elevator that's accelerating downward, the scale would show a lower reading than your actual weight.
📊 True Weight vs. Apparent Weight in Orbit
Here’s a table comparing true weight and apparent weight, specifically focusing on orbiting scenarios:
| Feature |
True Weight |
Apparent Weight |
| Definition |
The gravitational force exerted on an object. |
The force experienced by the object due to support reactions (e.g., a scale or the floor). |
| Calculation |
$W = mg$ (where $m$ is mass and $g$ is the local gravitational acceleration). More precisely: $F = G \frac{m_1m_2}{r^2}$ |
The normal force exerted on the object by its surroundings. If no supporting force, apparent weight is zero. |
| In Orbit |
Significant; astronauts still experience gravitational pull from Earth. It's about 90% of what it is on Earth. |
Near zero; astronauts are in a continuous state of freefall. |
| Cause of 'Weightlessness' in Orbit |
Gravitational force |
Freefall; the orbiting object and everything within it (like astronauts) are accelerating towards Earth at the same rate. |
| Measurement |
Calculated based on mass and gravitational field. |
Measured by a scale or force sensor. |
✨ Key Takeaways
- 🌍 True weight is the force of gravity acting on an object. It exists even in orbit.
- 🚀 Apparent weight is what you *feel* as weight, often due to support forces. It's near zero in orbit because of continuous freefall.
- 🤔 'Weightlessness' in orbit doesn't mean there's no gravity; it means objects are constantly falling together.
- 💡 Astronauts are still affected by Earth's gravity; that's what keeps them in orbit. They aren't floating because there's no gravity; they are floating because they are falling!