Asked by christian
Explain the effect of Earth’s gravity on objects on the surface of Earth.
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Answered by
GPT-5 mini
AI
Earth’s gravity is the attractive force that the planet exerts on masses at or near its surface. Its main effects on objects on Earth are:
- Force and direction
- Every object of mass m feels a gravitational force toward Earth’s center: F = G M_e m / r^2, which near the surface is well-approximated by F = m g.
- g (standard gravitational acceleration) ≈ 9.81 m/s² downward.
- Weight and mass
- Weight is the gravitational force on an object: W = m g. Mass is an intrinsic property and does not change with location; weight does (with g).
- A scale measures the normal force balancing gravity when you stand still; that reading is your apparent weight.
- Motion under gravity
- In free fall (neglecting air resistance) all objects accelerate downward at g regardless of mass. This is why dropped objects speed up by about 9.81 m/s every second.
- Projectile motion (throws) is the combination of gravity (vertical acceleration) and any initial horizontal velocity.
- With air resistance, falling objects reach a terminal velocity where drag balances weight and acceleration stops.
- Energy
- Lifting an object increases its gravitational potential energy by ΔU ≈ m g Δh near Earth’s surface; letting it fall converts that energy into kinetic energy.
- Apparent-weight changes and normal force
- If you’re accelerating (e.g., in an elevator or car), the normal force differs from mg, so you feel lighter or heavier even though your mass is unchanged.
- In free fall (e.g., orbiting spacecraft), you feel weightless because the normal force is zero, even though gravity is still acting.
- Global variations and other effects
- g varies slightly with altitude (decreases with height) and latitude (slightly less at the equator because of Earth’s rotation and equatorial bulge).
- Earth’s gravity holds the atmosphere and oceans to the planet and determines pressure and hydrostatic balance.
In short: gravity gives objects weight, causes them to accelerate downward at about 9.81 m/s² when unsupported, governs falling and projectile motion, stores and releases gravitational potential energy, and keeps the atmosphere and oceans bound to Earth.
- Force and direction
- Every object of mass m feels a gravitational force toward Earth’s center: F = G M_e m / r^2, which near the surface is well-approximated by F = m g.
- g (standard gravitational acceleration) ≈ 9.81 m/s² downward.
- Weight and mass
- Weight is the gravitational force on an object: W = m g. Mass is an intrinsic property and does not change with location; weight does (with g).
- A scale measures the normal force balancing gravity when you stand still; that reading is your apparent weight.
- Motion under gravity
- In free fall (neglecting air resistance) all objects accelerate downward at g regardless of mass. This is why dropped objects speed up by about 9.81 m/s every second.
- Projectile motion (throws) is the combination of gravity (vertical acceleration) and any initial horizontal velocity.
- With air resistance, falling objects reach a terminal velocity where drag balances weight and acceleration stops.
- Energy
- Lifting an object increases its gravitational potential energy by ΔU ≈ m g Δh near Earth’s surface; letting it fall converts that energy into kinetic energy.
- Apparent-weight changes and normal force
- If you’re accelerating (e.g., in an elevator or car), the normal force differs from mg, so you feel lighter or heavier even though your mass is unchanged.
- In free fall (e.g., orbiting spacecraft), you feel weightless because the normal force is zero, even though gravity is still acting.
- Global variations and other effects
- g varies slightly with altitude (decreases with height) and latitude (slightly less at the equator because of Earth’s rotation and equatorial bulge).
- Earth’s gravity holds the atmosphere and oceans to the planet and determines pressure and hydrostatic balance.
In short: gravity gives objects weight, causes them to accelerate downward at about 9.81 m/s² when unsupported, governs falling and projectile motion, stores and releases gravitational potential energy, and keeps the atmosphere and oceans bound to Earth.
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