Types of Interactions and How to Detect Them
Zachary Schrack Fall '25
Interactions are when 2 or more things acting on each other in some way. This can be one object pushing another object, two planets pulling on each other with gravity, two electrons repelling each other, and many more types of interactions.
Main Idea
What are interactions?
Interactions are 2 or more things acting on each other in some way. This can be one object pushing another object, two planets pulling on each other with gravity, two electrons repelling each other, and many more types of interactions.
These interactions can often be identified as forces. These forces result from interactions. Like the interaction between two electric fields causes a force.
Types of Interactions
Basic types of Interactions
- Contact Interactions: and interaction between two objects that DO touch each other.
Ex: Tension, compression, friction, air resistance, collisions, ect.
- Non-Contact Interactions: any interaction between two objects that do NOT touch each other.
Ex: Gravitational fields, electric fields, magnetic fields, etc.
How to detect them
- Interactions cause a force on a object, and a force on an object can be detected by a change in velocity, either direction or magnitude. This is defined by newtons second law, F=ma. A force (or interaction) causes an acceleration (a change in velocity).
Ex: Gravitational interactions in the solar system can be detected by the change in direction of velocity caused by moving in an orbit.
- If an object is in equilibrium, it is more difficult to detect forces because there is no net change in velocity. However, in many problems, we can infer some forces are acting on an object, and determine what the other forces are to make Fnet=0.
Ex: in the case of an object in earth's atmosphere falling at terminal velocity. There is no change in velocity. Does that mean there are no forces? No, because we know the force of gravity is acting on it because it is near earth. Therefor there must be a force in the opposite direction to cancel out gravity, and we learn that is air resistance, which is a contact force (collisions of air molecules).
Mathematical Model
There are many mathematical models for every kind of interaction from universal gravity to the strong force within an atom. An example of one is the gravitation force equation. You cannot just apply one mathematical formula to every interaction in the universe, each type of interaction has its own formula and its own constants and variables. [math]\displaystyle{ F_{Gravity} = G \frac{m_1 m_2}{r^2} }[/math]
Computational Model
An example of a computational model would be this model of the 3 body problem using the gravitational interactions of 3 stars of equal mass. 3-Body Problem
Connectedness
- Engineering: In engineering, we work with all kinds of interactions from aerospace studying how an aircraft interacts with the air and the earth, to a chemical engineer studying the bond forces of different molecules. Many things in Engineering boil down to interactions in our world.
- Every Day Life: Our world is based on interactions, the trading of energy, the movement of nutrients in our bodies, electrical currents in our computers, chemical combustion in our cars. The universe is only hear because of interactions. Nuclear fission in stars created the elements we are made of, that is interactions.
History
Many of the physical interactions and the mathematical models that described them were pieced together by Sir Isaac Newton (1642-1727). His three basic laws of physics described the relationship between interactions and motion; he also described universal gravitational interactions, and helped create calculus which layer the foundations to describe future interactions in detail. Later, many other scientists added more mathematical models describing interactions over time.
Further Reading
Fundamental Interactions in Physics (Studies in the Natural Sciences)
External Links
Phet simulations provide a good virtual lab to test a lot of interactions in every day life. https://phet.colorado.edu/