In physics, force is the fundamental component to producing or changing motion. There are many different types of forces acting on an object that must be considered when describing its movement. Continue reading to learn more about them!
The most common description of a force in physics is a push or pull acting on an object. This causes it to change acceleration, which is how we see objects go from rest to movement, movement to rest, increase in speed, decrease in speed, or other types of changes in its motion.
Force is usually measured in Newtons (N). In physics, especially when making calculations, it's important to consider all types of forces that are being inflicted on an object. Besides from the blatant applied force (more on that later!), there are other invisible forces that affect the movement of the object.
Applied Force
Firstly, the most obvious type of force that can be accounted for is applied force. This is any push or pull coming from a specific person or other object. For example, if you were to open or close a book, an applied force is acting on the book, which is coming from your actions.
Gravitational Force
Another common force is gravitational force, also sometimes referred to as weight (W). Weight is different from mass because while mass measures the amount of matter in a substance, weight also accounts for the force of gravity that is acting on a person or object. Gravitational force is the force pulling objects down toward the center of the earth, and is calculated by multiplying the gravitational field strength (g, in meters per second squared, m/s²) by the atmosphere with the mass (in kilograms, kg) of the object (W = m * g). The gravitational field strength on Earth is approximately 9.81 m/s², but this may vary in different circumstances, such as if you're calculating gravitational force on other plants that have different magnitudes of gravity.
Normal Force
Thirdly, if there is a surface that is in contact with the object, that is considered normal force. Normal force can be described as the force that is supporting the object. For example, as your book is resting on a table, the table's surface is exerting normal force on your notebook to support it up against the force of gravity. Additionally, if you were to throw a ball against the wall, the wall would exert horizontal normal force on the ball to cause it to bounce back in the other direction.
Friction Force
When an object slides against a surface or is attempting to, friction force is acting in the opposite direction. This is why after you slide a book across the table, it eventually comes to a stop, as friction acts on it to decelerate its motion.
There are two types of friction: static and kinetic. Static friction is used to describe the friction that an object must overcome (starting from rest) to get into motion. On the other hand, kinetic friction acts on the object as it is in motion. The amount of friction force that exists between two objects or surfaces is influenced by the type of surfaces and the strength of which they are being pressed together. For instance, two smooth surfaces acting against each other would have less friction than two rougher surfaces.
There is a specific formula to calculate the amount of friction based on the normal force and the friction coefficient: Ff = µ • FN. (friction force = coefficient of friction * normal force) This makes sense because as the strength of normal force increases, the amount of friction force between the two surfaces increases as well.
Tension Force
Tension force is the specific type of force that is exerted through a rope, wire, cable, or string that is tightly pulled on opposite sides. Tension force acts in both directions of the string. For instance, when you are stretching a string of floss, there is tension force on both sides of the string from where you are pulling, which causes the floss to be stretched tightly and rest in a straight line.
Spring Force
Spring force is also another type of force specific to the type of object. Any time a spring is stretched or compressed, and is released back to its starting form, it exerts spring force on the object it is acting on. For instance, when a person bounces on a pogo stick, their weight causes the spring at the bottom to be compressed, and as the spring extends to its original length, the force causes the stick, and the person, to move upward.
Air Resistance Force
Lastly, air resistance force exists when an object is in free fall, or is falling with gravity being the only other force acting on its acceleration. The amount of air resistance acting on an object depends on its surface area and speed. This is why sky divers open their parachutes after they jump off, as it slows down their downward speed because it adds more surface area to the system.
Additionally, due to air resistance, at a certain point in their free fall, objects will begin to fall at a terminal velocity, which occurs when the force of air resistance exactly balances gravitational force, and the object's velocity is no longer accelerating.
Now, you can understand the role of forces in our daily lives. Thank you for reading!
References:
“Free Fall and Air Resistance.” The Physics Classroom, www.physicsclassroom.com/class/newtlaws/Lesson-3/Free-Fall-and-Air-Resistance.
“Types of Forces.” The Physics Classroom, www.physicsclassroom.com/class/newtlaws/Lesson-2/Types-of-Forces.
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