Gravitasi • Part 1: Hukum Newton Tentang Gravitasi, Gaya Gravitasi, Medan Gravitasi

Summary

This instructional video explains Newton’s law of universal gravitation and related concepts for high-school physics. It covers the gravitational force formula F = G·m1·m2/r², the vector nature of gravity and how to find resultants, and the gravitational field (field strength) g as force per unit mass. The presenter derives g at a planet’s surface (g = GM/R²) and at height h (g = GM/(R+h)²), shows how to compare gravity between different planets, and explains gravitational potential energy Ep = −GMm/r and gravitational potential V = −GM/r. Clear examples, units, and practical reminders about distances measured to a planet’s center make the material accessible.

Takeaways

• 🌍 Newton's Law of Universal Gravitation states that every object in the universe attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.
• ⚖️ The formula for gravitational force is F = G * (m1 * m2) / r², where G is the gravitational constant (6.67 × 10⁻¹¹ N·m²/kg²).
• 🔄 Gravitational forces act in pairs—each object exerts an equal and opposite force on the other, consistent with Newton’s Third Law of Motion.
• 📐 Gravitational force is a vector quantity; when multiple forces act, their resultant is found using vector addition methods.
• 🌌 A gravitational field is the region around a mass where another mass experiences a gravitational force.
• 📊 The strength of a gravitational field (g) is defined as the gravitational force per unit mass, expressed as g = F/m, with units of N/kg or m/s².
• 🪐 The formula for gravitational field strength due to a planet is g = G * M / r², where M is the planet’s mass and r is the distance from its center.
• 🏔️ At a height h above a planet’s surface, the gravitational field strength becomes g' = G * M / (R + h)², where R is the planet’s radius.
• ⚖️ The ratio of gravitational field strengths at two planets or locations can be compared using formulas derived by dividing their respective g equations.
• 💡 Gravitational potential energy is given by Ep = -G * M * m / r, measured in joules, where the negative sign indicates attraction.
• 📉 Gravitational potential (V) is defined as V = Ep / m = -G * M / r, measured in joules per kilogram, and it is a scalar quantity.
• ➕ Unlike vector quantities like force and field strength, gravitational potentials from multiple sources can be added algebraically without considering direction.

Q & A

What is Newton's law of gravitation?

Newton's law of gravitation states that every object in the universe attracts every other object with a force that 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 gravitational force between two masses?

The formula for gravitational force is F = G * (m1 * m2) / r^2, where F is the gravitational force, G is the gravitational constant (6.67 × 10^-11 N m²/kg²), m1 and m2 are the masses of the two objects, and r is the distance between their centers.

What does it mean that gravitational force is a vector quantity?

Gravitational force is a vector quantity, meaning it has both magnitude and direction. If there are multiple forces acting on an object, their resultant gravitational force is calculated using vector addition, considering both the magnitude and direction of each force.

What is gravitational field strength?

Gravitational field strength is the force per unit mass experienced by an object in a gravitational field. It is also known as gravitational acceleration (denoted by 'g') and is measured in N/kg.

How is gravitational field strength calculated?

Gravitational field strength (g) is calculated using the formula g = F/m, where F is the gravitational force and m is the mass of the object experiencing the force.

What is the difference between gravitational force and gravitational field?

Gravitational force refers to the attractive force between two masses, whereas gravitational field refers to the region around a mass where other objects will experience a gravitational force. The field strength is the intensity of this force per unit mass.

What is the formula for gravitational field strength at the surface of a planet?

At the surface of a planet, the gravitational field strength is given by g = G * M / R², where G is the gravitational constant, M is the mass of the planet, and R is the radius of the planet.

How does gravitational field strength change with height above the surface of a planet?

At a height 'h' above the surface of a planet, the gravitational field strength is reduced. The formula is g' = G * M / (R + h)², where R is the radius of the planet, and h is the height above the surface.

What is the difference between gravitational potential energy and gravitational potential?

Gravitational potential energy is the energy an object possesses due to its position in a gravitational field, calculated as Ep = -G * M * m / r. Gravitational potential, on the other hand, is the potential energy per unit mass, calculated as V = Ep / m, and it is a scalar quantity.

How is gravitational potential energy used in problems involving height differences?

Gravitational potential energy is used to calculate the energy change as an object moves in a gravitational field. If an object moves to a higher height, its potential energy increases. The change in potential energy is given by ΔEp = -G * M * m * (1/r_initial - 1/r_final).