# Forces and Interactions | Science

January 28, 2016

Forces and Interactions | Science

What is a force? What is an interaction? And, together, what do they result in? As you continue to prepare for the TASC Test Assessing Secondary Completion™ Science subtest, let’s understand these physics topics further.

First, it’s beneficial to understand these terms separately:

• A force is a push or pull on an object from the object’s interaction with another object.
• An interaction is the way in which matter, fields, atomic, and subatomic particles affect one another.

According to PhysicsClassroom.com, “Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction [stops], the two objects no longer experience the force. Forces only exist as a result of an interaction.

PhysicsClassroom.com points out that all forces and interactions between objects can be understood in two ways: contact forces and action-at-a-distance forces.

Contact forces develop when two interacting objects are touching each other. Examples of contact forces include:

• Frictional forces
• Tensional forces
• Air resistance forces
• Applied forces
• Spring forces

Action-at-a-distance forces develop regardless if two interacting objects are touching each other. These forces are able to apply a push or pull despite their physical separation. Examples of action-at-a-distance forces include:

• The sun and planets with gravitational pull, despite how far apart they are
• You – jumping in the air – and the Earth with gravitational pull
• Electric forces, since protons and electrons have an electrical pull toward each other even though they are separated by the nucleus of an atom
• Magnetic forces, since magnets pull toward each other even when separated by a small distance

When discussing forces and interactions, it’s also important to review Newton’s First and Third Laws of Motion.

• Newton's First Law of Motion states that an object in motion will remain in motion unless acted on by an outside force.
• For example, let’s say you’re riding your bicycle (object in motion) when you suddenly hit the curb of the road (outside force). This interaction may cause you to fall off of your bike, abruptly stopping the motion of the bike.
• Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction.
• For example, when you sit in a chair, your body applies a downward force on the chair, and the chair applies an upward force on your body.
• Every interaction has two forces. The size of the first force (you sitting in a chair) equals the size of the second force (the chair applying upward force to support you).
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