In very basic terms, a force is a push or a pull. Forces can be measured by either measuring a change in the size and/or shape of an object or by measuring the change in the speed or direction of an object.
Forces can be combined and can do some amazing things. They can change an objects velocity, make things turn, do work, make things move in a circle. Forces can hold particles together, cause oscillations and allow us to fly.
There are a number of different forces that can act on an object. There are divided into two relatively broad categories – contact forces, where there is physical contact between two objects; and action-at-distance forces or forces not requiring contact between the objects.
Contact forces include the following: Applied Force is a force applied to an object by another object or person. One example of this type of force is pushing a couch across a floor. The couch moves as a result of the force exerted on it by the person pushing it.
Frictional Force is a force exerted by a surface as an object moves across it. It opposes the direction of the object. One example of this is when a customer orders a beer like in the old time movies and the bartender slides the beer down the bar. The bar exerts a force in the form of fiction in the opposite direction of the motion of the beer, causing it to stop.
Air Resistance Force is a type of frictional force exerted on objects when they travel through the air. Like frictional forces, it opposes the motion of the object. This type of force is most noticed when objects travel at high speeds or objects that have a large surface area. Some athletes look at air resistance like in skydiving or downhill skiing or even NASCAR drivers and look for different equipment or clothing to reduce the air resistance forces.
Normal Force is a support force exerted on an object in contact with another stable object. Example is the upward force applied by a bench to support a person’s weight. Also, a normal force can be horizontally exerted between two objects that are in contact with each other.
Tensional Force is transmitted through a rope or wire when it is stretched tightly between two objects. One obvious example here would be a tug of war with two teams on either end of a rope.
Spring Force is the force exerted by a compressed or stretched spring on the object to which it is attached. This restores the object to its rest position. For the majority of springs, the magnitude that the force exerts is directly proportional to the stretch or compression. One example here is to think about a rubber band and what you feel when pulling it back and forth.
Forces which act at a distance, or, in other words, forces that are exerted without actual contact include: Gravitational Force – essentially the weight of an object. It is the force with which the earth or another huge body like the moon attracts an object toward itself. Weight is a measure of that force. Because of many factors, mass being the predominant, we would weigh about six times less on the moon than on earth.
Electrical force is another kind of force that can act at a distance. Electrical force is simply the negative charges from electrons and positive charges from protons. The protons are attracted to the negative electrons and have a kind of attractive force to the electrons. The effect of this electrical force is relatively negligible in ordinary situations.
Magnetic forces are also a kind of an at a distance force. Magnetism force has an electrical charge when moving in a magnetic field. The size of the magnetic force is proportional to the electrical charge and to the velocity as well as to the magnetic field and it depends on the direction of the vectors.
All of these forces play a role with respect to objects in motion and at rest. For example, a golf ball about to be hit from a tee is essentially at rest, meaning all of the forces affecting it are in balance. Hitting applies force and it accelerates.
At once, other forces such as gravity and air resistance begin to operate to slow down the acceleration and reduce the velocity such that eventually the ball lands, which slows it further due to the friction of the ground, and eventually it comes to rest again.
Depending on how the ball is hit, there can be directional forces operating as well, forces that will cause the ball to go right or left. These occur when the golfer cuts across the ball during the swing, rather than hitting it straight. A slice or hook can result. Also because the club is grooved, hitting down on the ball can impart backspin as well as a driving force forward. When the ball lands, it can stop suddenly or even roll backwards because the force of the back-spinning ball interacts with the normal frictional force to cause a reverse of direction. Now, go out and shoot par or better and rely on physics!