Problem 15 - Basic Physics: A Self-Teaching Guide

Question

Your weight is the result of the earth's downward gravitational force on your body. What is the corresponding reaction force? ___________

Step-by-Step Solution

Answer

The reaction force is your body pulling upward on the Earth with an equal magnitude.

Step 1: Identify the given information

Understand that the exercise describes your weight as the result of the Earth's gravitational force on your body.

Step 2: Apply Newton's Third Law

According to Newton's Third Law of Motion, for every action, there is an equal and opposite reaction.

Step 3: Determine the reaction force

The action force is the Earth's gravitational pull on your body (your weight). The reaction force is your body pulling upward on the Earth with an equal magnitude.

Key Concepts

Gravitational Force

Gravitational force is a fundamental force of nature that attracts two bodies toward each other. This force is what keeps the planets in orbit around the sun and causes objects to fall to the ground when dropped. It acts between any two masses, and its strength is directly proportional to the product of the masses and inversely proportional to the square of the distance between them. The formula for gravitational force is given by Newton's law of gravitation: \[F = G \frac{m_1 m_2}{r^2}\]Where:

• \(F\) is the gravitational force.
• \(G\) is the gravitational constant (\(6.674 \times 10^{-11} \) Nm²/kg²).
• \(m_1\) and \(m_2\) are the masses of the two objects.
• \(r\) is the distance between the centers of the two masses.

In the context of the exercise, the Earth exerts a gravitational force on your body, which is commonly referred to as your weight. This force pulls you towards the center of the Earth.

Action-Reaction Pairs

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that forces always come in pairs, known as action-reaction pairs. When one object exerts a force on another, the second object exerts an equal and opposite force back on the first object. This law ensures that forces are balanced and interactions between objects are mutual.In the context of the exercise, your weight is the result of the Earth's gravitational force acting on your body. Therefore, the action force is the Earth pulling you downward with a certain force. According to Newton's Third Law, the reaction force is your body pulling upward on the Earth with an equal magnitude. Although your body is much smaller than the Earth, the forces are equal in strength but opposite in direction.

Weight

Weight is the force exerted by gravity on an object's mass. It is the product of an object's mass and the gravitational acceleration. The formula for calculating weight is:\[W = mg\]Where:

• \(W\) is the weight of the object.
• \(m\) is the mass of the object.
• \(g\) is the acceleration due to gravity (approximately \(9.8\) m/s² on Earth).

In the exercise, your weight is the force that the Earth's gravity exerts on your body. This force is always directed towards the center of the Earth. Weight can vary depending on the gravitational field strength, which is why you would weigh differently on different planets. However, mass remains constant irrespective of location. Understanding weight as a force explains why our body pushes back against the Earth with an equal force, creating the reaction force mentioned in the exercise.