Purpose: To explore the fundamental forces in the universe

Introduction: In the previous lesson, you viewed the MUHSA video The Fundamental Forces. You learned that the equation for Newton's Law of Universal Gravitation and the equation for Coulomb's Law were strikingly similar. In this activity you will explore a tutorial and review problems utilizing both equations.

Materials: scientific calculator

Procedure:

1. Read and study the tutorial on Newton's Law of Universal Gravitation and Coulomb's Law. You will want to print a copy for your notebook.

2. To solve problems involving these laws you will need to know how to enter numbers into your calculator that are expressed in scientific notation. Please review the instructions that came with your calculator. If you have any questions regarding the use of your calculator or the tutorial, please email.

Tutorial:

Part 1 - Newton's Law of Universal Gravitation

1. Newton's interest in mechanics was rekindled with the advent of a spectacular comet in 1680 and another two years later. His friend Edmond Halley, for whom the second comet was later named, suggested that he return to work on a previously unverified idea about the motion of the moon. Newton made corrections to his experimental data, obtained excellent results, and published his findings: The Law of Universal Gravitation.

   1. Newton's Law of Universal Gravitation states, "every mass in the universe attracts every other mass in the universe with a force that is directly proportional to the product of the two masses involved and is inversely proportional to the square of the distance separating them."

2. Here is a sample problem: The earth and the sun are 1.5 E 11 meters apart. Use Newton's Law of Universal Gravitation to calculate the force of gravity between the earth (mass = 6.0 E 24 kg) and the sun (mass = 2.0 E 30 kg).

Work:
F_g = (Gm₁m₂)/d²

F_g = [(6.67 E -11 N*m²/kg² )(6.0 E 24 kg)
(2.0 E 30 kg)]/(1.5 E 11 m)²

Hint: These are "easy," but "messy" calculations. Use proper grouping symbols.

3. Look at the answer in part B. Is this the force the earth exerts on the sun or is this the force that the sun exerts on the earth? Think about Newton's Third Law. Remember that forces come in equal and opposite pairs. The gravitational force from part B, 3.6 E 22 N, is the force that the earth exerts on the sun AND the force that the sun exerts on the earth. The forces are the same magnitude, but are in opposite directions.

Part 2 - Coulomb's Law

2. The electric force, like gravitational force, decreases inversely as the square of the distance between charges. However, even though the gravitational force of attraction between particles such as an electron and a proton is extremely small, the electrical force between these particles is relatively enormous. The relationship that explains the force between charged particles was discovered by Charles Coulomb in the eighteenth century.

   1. Coulomb's Law of electrical forces states, "for charged particles that are smaller than the distance between them, the force between two charges varies directly as the product of the charges and inversely as the square of the separation distance. The force acts along a straight line from one charge to the other."

2. Here is a sample problem: Jenny loves puffed rice cereal. As she is pouring the cereal, two little pieces of cereal each with equal charges of 1.85 E -18 coulombs fall into the bowl 0.025 meters apart. Use Coulomb's Law to find the electrostatic force between them.