Force of Attraction: Formula & Concept

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  • 0:01 Force of Attraction Defined
  • 2:28 Forces of Attraction: Formula
  • 4:09 Lesson Summary
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Lesson Transcript
Instructor: Richard Cardenas

Richard Cardenas has taught Physics for 15 years. He has a Ph.D. in Physics with a focus on Biological Physics.

In this lesson, you will learn about the force of attraction and the kinds of forces that cause attraction. You will learn the formulas for these forces and learn how to calculate the force of attraction in each case, and learn about the properties of each force of attraction.

Force of Attraction Defined

I'm sure you have heard the statements, 'What goes up must come down' and 'opposites attract'. In physics, they refer to forces of attraction. So what is a force of attraction and how many types of these forces are out there?

A force of attraction is any type of force that causes objects to come together, even if those objects are not close to or touching each other. The first force that causes attraction is the gravitational force. According to Newton's Universal Law of Gravitation, every object in the universe attracts every other object in the universe. Gravity is an attractive force since any object with mass will experience a force of attraction from other objects with mass. Gravity is the reason for the statement 'What goes up must come down.'

The second force that can cause attraction is the electric force, also known as the electrostatic force. While gravity affects objects with mass, electrostatic forces affect objects that have charge. Charge is determined by the number of electrons and protons in an object. Most objects are electrically neutral, which means they have an equal amount of electrons, which carry a negative charge, and protons, which carry a positive charge. But sometimes, objects can lose electrons and be positively charged, or gain electrons and become negatively charged. The attraction occurs when two objects of opposite charge are in close proximity, and the electrical force causes these objects to attract. Therefore, positive and negative charges will attract each other. Hence the saying 'Opposites attract.'

The third force that may cause attraction is the magnetic force. The magnetic force attracts objects that have magnetic properties. A magnet will attract metals rich in iron, like steel, as well as nickel and cobalt. But when an object is magnetized, the magnetic force is attractive when a north magnetic pole is brought into close proximity to a south magnetic force. The main source of magnetism is electric currents. When charges move, there is an electric current. So charges that don't move are affected by the electric force and charges that move are affected by the magnetic force. Magnetic attraction can also be the reason behind the saying 'Opposites attract.'

Formulas for the Forces of Attraction

There are several formulas for the forces of attraction. First, let us look at the force of gravity. Every object in the universe attracts every other object in the universe. This figure shows two objects separated by a distance r.

The force of gravitational attraction is proportional to the product of the masses, m1 and m2, and is inversely proportional to the square of the distance between the two masses, represented by r. Inversely proportional means that the attraction is strong when the masses are close to each other and weak when the masses are far away from each other.

The force of electrical attraction is proportional to the product of the charges and just like gravitation, it is inversely proportional to the square of the distance between the charges. This figure shows the attraction between a positive and a negative charge separated by a distance r.

Just like the gravitational force, when the charges are close to each other, the force is stronger, and when the charges are further away, the force is weaker.

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