3A4 Gravitation Flashcards
Describe how Newton's law of universal gravitation relate to the concepts of satellites, orbital motion, and acceleration.
What does Newton’s law of universal gravitation state?
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.
What is the formula for the gravitational force between two masses?
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.
What is the value of the universal gravitational constant G?
6.67×10^(−11) Nm²/kg²
G is a very small number, indicating that gravity is a weak force compared to others like electromagnetism.
What experiment determined the universal gravitational constant (G)?
The Cavendish experiment
It used a torsion balance to measure the gravitational force between small masses.
True or false:
The gravitational force between two objects decreases as the distance between them increases.
True
This is due to the inverse square relationship in Newton’s law of universal gravitation.
How does the gravitational force change if the mass of one object doubles?
The gravitational force also doubles.
This is because force is directly proportional to the product of the two masses.
What happens to the gravitational force if the distance between two objects is halved?
The gravitational force increases by a factor of four.
This follows the inverse square law: F ∝ 1/r²
Why is gravitational force considered a non-contact force?
Because it acts at a distance without physical contact between objects.
This is also true for forces like magnetism and electrostatic force.
True or false:
Gravitational force only acts on large objects like planets and stars.
False
Gravitational force acts on all objects with mass, regardless of size.
How does gravity influence matter at the atomic scale?
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.
What is the direction of the gravitational force between two objects?
Along the line connecting their centers of mass.
Gravity acts between centers of mass, as per Newton’s law.
Fill in the blank:
Gravitational force is a ______ force because it only attracts objects.
conservative
Conservative forces have potential energy associated with them and depend only on initial and final positions.
Why do we not feel the gravitational pull of small objects like a table?
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.
True or false:
Gravitational force is responsible for the tides on Earth.
True
Tides result from the gravitational pull of the Moon and the Sun on Earth’s oceans.
What celestial phenomena are examples of gravitational force?
- 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.
What is acceleration due to gravity?
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.
How does acceleration due to gravity vary with altitude?
It decreases as altitude increases.
Gravity weakens with distance from the center of Earth.
Fill in the blank:
Gravity affects an object’s _______, like in roller coasters.
acceleration
Gravity changes velocity, particularly in free-fall scenarios.
Define:
Orbit
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.
Define:
Satellite
Object that orbits a planet or other celestial body.
Satellites can be natural, like moons, or artificial, like communication satellites.
What is the difference between a natural satellite and an artificial satellite?
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.
How are artificial satellites positioned in orbit?
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.
Why do satellites remain in orbit instead of falling?
Their speed counteracts gravity, keeping them in orbit.
This balance creates a stable orbit around Earth.
How does an orbit relate to Newton’s Law of Universal Gravitation?
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.
Fill in the blank:
The ______ of a satellite depends on the balance between gravitational pull and orbital velocity.
orbit
Orbital shape and stability depend on velocity and altitude.
True or false:
A geostationary satellite orbits the Earth in 24 hours.
True
Geostationary satellites match Earth’s rotation, appearing stationary in the sky.
Why do satellites closer to Earth need to move faster?
To counteract the stronger gravitational pull closer to Earth.
Orbital speed increases as the distance to Earth decreases.
What happens if a satellite’s speed is too low?
It will fall back to Earth due to insufficient centripetal force.
Gravity overcomes the satellite’s inertia if velocity is too low.
Fill in the blank:
Satellite ______ is used for navigation, communication, and weather monitoring.
technology
Satellites serve diverse roles, from GPS to climate studies.
Fill in the blank:
Gravity provides the ______ ______ that keeps satellites in orbit.
centripetal force
Satellites stay in motion because gravity pulls them toward Earth, balancing their velocity.
Why is gravity weaker on the Moon compared to Earth?
The Moon’s lower mass creates weaker gravity.
Gravitational force is directly proportional to the mass of the celestial body.
Why does the Moon stay in orbit around Earth?
Because Earth’s gravity provides the centripetal force needed to keep it in orbit.
Orbital motion results from the balance between gravity and the Moon’s inertia.
Explain the concept of weightlessness in space.
It occurs when an object is in free-fall, orbiting Earth, and the gravitational force is balanced by the orbital motion.
Astronauts appear weightless because they are in continuous free-fall around Earth.
Explain why the International Space Station remains in orbit.
It moves fast enough to avoid falling while gravity continuously pulls it toward Earth.
This balance creates a state of continuous free-fall.
Why are polar orbits useful for mapping Earth?
They allow satellites to cover the entire surface as Earth rotates.
They cross both poles every orbit, covering the entire planet.
True or false:
Satellites experience air resistance in outer space.
False
In outer space, there is no significant atmosphere to cause drag.
Define:
Gravitational field
The area around a mass where it exerts gravitational force.
Its strength is expressed as g=F/m
How do gravitational fields affect objects in space?
These fields keep celestial bodies in orbit by exerting forces on them.
Fields act over vast distances, binding solar systems and galaxies.
What is the value of acceleration due to gravity on Earth?
9.8 m/s²
This is the average value near Earth’s surface.
Fill in the blank:
Gravitational field strength is proportional to an object’s ______.
mass
Gravitational field strength also decreases with distance squared.
True or false:
All objects fall at the same rate in a vacuum.
True
Air resistance is absent in a vacuum, so objects experience only gravity.
Why does a feather fall slower than a stone in air?
Air resistance affects the feather more than the stone since the feather has a larger surface area.
Lighter, larger objects face greater air drag.
How does the gravitational field of Earth compare to that of Jupiter?
Jupiter’s gravitational field is stronger due to its larger mass.
Larger celestial bodies exert stronger gravitational forces.
True or false:
The gravitational field inside a hollow sphere is zero.
True
Symmetry cancels out forces inside a hollow sphere.
True or false:
Gravity plays a role in the operation of pendulum clocks.
True
Gravity creates the restoring force that enables the pendulum’s periodic motion, crucial for timekeeping.
Fill in the blank:
Gravity allows for the measurement of ______ by weighing objects.
mass
Weight is the gravitational force acting on an object, directly proportional to its mass.
How does gravity contribute to the formation and use of hydroelectric power?
Gravity causes water to flow from high reservoirs to lower turbines, generating kinetic energy for electricity.
The potential energy of elevated water is converted into electricity using gravity.
