3A4 Gravitation

Question 1

What does Newton’s law of universal gravitation state?

Answer 1

Every object in the universe attracts every other object with mass.

This attraction is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Question 2

What is the formula for the gravitational force between two masses?

Answer 2

F = [G * (m1 * m2)] / r²

F is the gravitational force,
G is the Universal gravitational constant,
m1 and m2 are masses,
and r is the radius between the masses.

Question 3

What is the value of the universal gravitational constant G?

Answer 3

6.67×10^(−11) Nm²/kg²

G is a very small number, indicating that gravity is a weak force compared to others like electromagnetism.

Question 4

What experiment determined the universal gravitational constant (G)?

Answer 4

The Cavendish experiment

It used a torsion balance to measure the gravitational force between small masses.

Question 5

True or false:

The gravitational force between two objects decreases as the distance between them increases.

Answer 5

True

This is due to the inverse square relationship in Newton’s law of universal gravitation.

Question 6

How does the gravitational force change if the mass of one object doubles?

Answer 6

The gravitational force also doubles.

This is because force is directly proportional to the product of the two masses.

Question 7

What happens to the gravitational force if the distance between two objects is halved?

Answer 7

The gravitational force increases by a factor of four.

This follows the inverse square law: F ∝ 1/r²

Question 8

Why is gravitational force considered a non-contact force?

Answer 8

Because it acts at a distance without physical contact between objects.

This is also true for forces like magnetism and electrostatic force.

Question 9

True or false:

Gravitational force only acts on large objects like planets and stars.

Answer 9

False

Gravitational force acts on all objects with mass, regardless of size.

Question 10

How does gravity influence matter at the atomic scale?

Answer 10

It plays a negligible role at the atomic scale because the electromagnetic and nuclear forces are significantly stronger than gravitational force between atoms.

While gravity dominates at large scales (e.g., planets, stars), its effect at the atomic scale is too weak to impact atomic or molecular interactions.

Question 11

What is the direction of the gravitational force between two objects?

Answer 11

Along the line connecting their centers of mass.

Gravity acts between centers of mass, as per Newton’s law.

Question 12

Fill in the blank:

Gravitational force is a ______ force because it only attracts objects.

Answer 12

conservative

Conservative forces have potential energy associated with them and depend only on initial and final positions.

Question 13

Why do we not feel the gravitational pull of small objects like a table?

Answer 13

Because their masses are too small to exert a noticeable gravitational force.

The gravitational constant (G) is very small, making the force negligible for small masses.

Question 14

True or false:

Gravitational force is responsible for the tides on Earth.

Answer 14

True

Tides result from the gravitational pull of the Moon and the Sun on Earth’s oceans.

Question 15

What celestial phenomena are examples of gravitational force?

Answer 15

• Moon revolving around the Earth
• Planets revolving around the Sun
• Solar system revolving around the Milky Way

Gravity is the key force shaping the structure and dynamics of the universe, from solar systems to galactic formations.

Question 16

What is acceleration due to gravity?

Answer 16

The increasing speed of an object as it approaches the ground under the influence of gravity.

This acceleration occurs due to the Earth’s large mass, attracting objects towards it.

Question 17

How does acceleration due to gravity vary with altitude?

Answer 17

It decreases as altitude increases.

Gravity weakens with distance from the center of Earth.

Question 18

Fill in the blank:

Gravity affects an object’s _______, like in roller coasters.

Answer 18

acceleration

Gravity changes velocity, particularly in free-fall scenarios.

Question 19

Define:

Orbit

Answer 19

Curved path of an object around a point in space, caused by gravitational forces.

Common examples include planets orbiting the Sun and moons orbiting planets.

Question 20

Define:

Satellite

Answer 20

Object that orbits a planet or other celestial body.

Satellites can be natural, like moons, or artificial, like communication satellites.

Question 21

What is the difference between a natural satellite and an artificial satellite?

Answer 21

Natural satellites are formed through natural processes, while artificial ones are created for specific purposes like communication or research.

E.g., the Moon naturally orbits the Earth while the Hubble space telescope has been placed in orbit.

Question 22

How are artificial satellites positioned in orbit?

Answer 22

They are launched with enough speed and at the correct angle to achieve a stable orbit, balancing gravity and inertia.

The required velocity depends on the altitude and gravitational force of the planet.

Question 23

Why do satellites remain in orbit instead of falling?

Answer 23

Their speed counteracts gravity, keeping them in orbit.

This balance creates a stable orbit around Earth.

Question 24

How does an orbit relate to Newton’s Law of Universal Gravitation?

Answer 24

An orbit occurs when an object’s forward velocity balances the gravitational pull of a larger body, creating a stable curved path.

Gravity provides the centripetal force required for orbital motion.

Question 25

# Fill in the blank: The \_\_\_\_\_\_ of a satellite depends on the **balance** between **gravitational pull** and **orbital velocity**.

Answer 25

orbit ## Footnote Orbital shape and stability depend on velocity and altitude.

Question 26

# True or false: A **geostationary satellite** orbits the Earth in 24 hours.

Answer 26

True ## Footnote Geostationary satellites match Earth’s rotation, appearing stationary in the sky.

Question 27

Why do **satellites** closer to Earth need to **move faster**?

Answer 27

To **counteract** the stronger **gravitational pull** closer to Earth. ## Footnote Orbital speed increases as the distance to Earth decreases.

Question 28

What happens if a satellite’s **speed** is too **low**?

Answer 28

It will **fall back** to Earth due to insufficient centripetal force. ## Footnote Gravity overcomes the satellite's inertia if velocity is too low.

Question 29

# Fill in the blank: Satellite \_\_\_\_\_\_ is used for **navigation**, **communication**, and **weather monitoring**.

Answer 29

technology ## Footnote Satellites serve diverse roles, from GPS to climate studies.

Question 30

# Fill in the blank: **Gravity** provides the \_\_\_\_\_\_ \_\_\_\_\_\_ that keeps satellites in orbit.

Answer 30

centripetal force ## Footnote Satellites stay in motion because gravity pulls them toward Earth, balancing their velocity.

Question 31

Why is **gravity weaker on the Moon** compared to Earth?

Answer 31

The Moon’s **lower mass** creates weaker gravity. ## Footnote Gravitational force is directly proportional to the mass of the celestial body.

Question 32

Why does the **Moon** stay in **orbit** around Earth?

Answer 32

Because Earth’s gravity provides the **centripetal force** needed to keep it in orbit. ## Footnote Orbital motion results from the balance between gravity and the Moon's inertia.

Question 33

Explain the concept of **weightlessness** in space.

Answer 33

It occurs when an object is in **free-fall**, orbiting Earth, and the gravitational force is balanced by the orbital motion. ## Footnote Astronauts appear weightless because they are in continuous free-fall around Earth.

Question 34

Explain why the **International Space Station** remains in orbit.

Answer 34

It **moves fast enough** to avoid falling while gravity continuously pulls it toward Earth. ## Footnote This balance creates a state of continuous free-fall.

Question 35

Why are **polar orbits** useful for mapping Earth?

Answer 35

They allow satellites to **cover** the entire surface as Earth rotates. ## Footnote They cross both poles every orbit, covering the entire planet.

Question 36

# True or false: Satellites experience **air resistance** in outer space.

Answer 36

False ## Footnote In outer space, there is no significant atmosphere to cause drag.

Question 37

# Define: Gravitational field

Answer 37

The **area around a mass** where it exerts gravitational force. ## Footnote Its strength is expressed as g=F/m

Question 38

How do **gravitational fields** affect objects in space?

Answer 38

These fields keep celestial bodies **in orbit** by exerting forces on them. ## Footnote Fields act over vast distances, binding solar systems and galaxies.

Question 39

What is the value of acceleration due to **gravity on Earth**?

Answer 39

9.8 m/s² ## Footnote This is the average value near Earth’s surface.

Question 40

# Fill in the blank: Gravitational field strength is **proportional** to an object’s \_\_\_\_\_\_.

Answer 40

mass ## Footnote Gravitational field strength also decreases with distance squared.

Question 41

# True or false: All objects fall at the same rate in a **vacuum**.

Answer 41

True ## Footnote Air resistance is absent in a vacuum, so objects experience only gravity.

Question 42

Why does a **feather** fall slower than a **stone** in air?

Answer 42

**Air resistance** affects the feather more than the stone since the feather has a larger surface area. ## Footnote Lighter, larger objects face greater air drag.

Question 43

How does the **gravitational field** of Earth compare to that of **Jupiter**?

Answer 43

Jupiter’s gravitational field is **stronger** due to its larger mass. ## Footnote Larger celestial bodies exert stronger gravitational forces.

Question 44

# True or false: The **gravitational field** inside a **hollow** sphere is zero.

Answer 44

True ## Footnote Symmetry cancels out forces inside a hollow sphere.

Question 45

# True or false: **Gravity** plays a role in the operation of **pendulum clocks**.

Answer 45

True ## Footnote Gravity creates the restoring force that enables the pendulum's periodic motion, crucial for timekeeping.

Question 46

# Fill in the blank: **Gravity** allows for the measurement of \_\_\_\_\_\_ by weighing objects.

Answer 46

mass ## Footnote Weight is the gravitational force acting on an object, directly proportional to its mass.

Question 47

How does **gravity** contribute to the formation and use of **hydroelectric power**?

Answer 47

Gravity causes water to flow from high reservoirs to lower turbines, generating **kinetic energy** for electricity. ## Footnote The potential energy of elevated water is converted into electricity using gravity.