Force (physics)
In physics, force is defined as any interaction that causes an object to change its motion or velocity. This encompasses a wide range of influences, such as pushing or pulling actions, which can alter the speed and direction of an object. Force is quantitatively measured in Newtons and can be calculated using the formula F = ma, where F represents force, m is mass, and a is acceleration. Various types of forces affect motion, including applied force, gravity, friction, and normal force.
Sir Isaac Newton's three laws of motion provide a foundational framework for understanding how force operates. His first law, the law of inertia, states that an object at rest will remain at rest unless acted upon by an external force. The second law indicates that greater mass requires more force for acceleration, while the third law asserts that every action has an equal and opposite reaction. Additionally, the concept of elasticity, articulated by Robert Hooke, describes how objects deform under force and return to their original shape when the force is removed.
Overall, force is a fundamental concept in physics that explains how objects interact and move in the universe, encompassing both contact and action-at-a-distance forces.
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Subject Terms
Force (physics)
In physics, force is characterized as any influence or interaction by one object on another object, which results in force being exerted on both objects, as well as changes in the motion and the velocity. Velocity is defined as the rate at which a physical object changes position. When the velocity of an object is changing, the word "acceleration" is used. For example, the action involved in pushing a door open or pulling it closed serves as the force that influences the door to change its velocity (to accelerate or decelerate) and its direction. Force is measured in units called Newtons, and the total amount of force (F) can be determined by multiplying an object’s mass (m) by the amount of its acceleration (a), expressed by the equation F = ma.
Gravity is a naturally occurring force that exists in varying strengths throughout the universe. On Earth, the gravitational pull effects objects on or surrounding the planet. For example, when a ball is bouncing, the force of gravity works to slow the ball down as it is going up, but when the ball begins to return to the ground, the force of gravity accelerates the downward motion of the ball.
Brief History
Sir Isaac Newton (1643–1727), an English physicist and mathematician, studied the motion of objects and found that all objects in motion are affected by certain laws. These laws, which he outlined in 1687, are referred to as Newton’s three laws of motion.
Newton’s first law of motion, also called the law of inertia, states that a resting object will tend to stay at rest because an object’s motion cannot be initiated without an external force acting on it. An object that is already in motion, however, will tend to stay in motion and will continue to go in the same direction and at the same acceleration until a force is applied to it that then affects its direction and/or acceleration.
Newton’s second law of motion deals with the size of an object, the force applied to it, and its resulting rate of acceleration. The second law shows that the greater the mass of the object, the greater the amount of force needed to accelerate the object. Put simply, objects that are heavier will require more force to move than objects that are lighter, and if the same amount of force is applied to two objects of different mass, the acceleration will be more noticeable in the object with a smaller mass than in the object with a larger mass.
Newton’s third law of motion illustrates the statement that for every action there is an equal and opposite reaction. In other words, every time force is applied to an object from one direction, an equal amount of force will be dispersed onto the object in the opposite direction. This principle can be seen in the example of a rocket launch: When a rocket is launched, it is pushed through the air by the force of the explosion at the same time that it is being pushed back toward the earth by the force of gravity.
Overview
Hooke’s law was named after seventeenth-century English scientist Robert Hooke (1635–1703), who discovered the law of elasticity in 1660 and the effect of force on solid matter. The law states that when a force is applied to a solid object, a deformation of the object or a displacement of its matter takes place. The size of the deformation or displacement is therefore directly proportional to the amount of force (or load) that is applied to the object. The resulting elasticity occurs when the force is removed and the object regains its original or natural shape, despite being stretched, compressed, bent, twisted, or squeezed. For example, when a wet sponge is squeezed and twisted in order to remove the water, the original shape of this solid object is deformed by the applied pressure or force. However, when the force is removed, such as when the sponge is no longer being squeezed, the sponge returns to its original state and shape. This is the concept of Hooke’s theory of elasticity.
Additionally, two other concepts can also be used to describe types of force: stress and strain. Stress is defined as a force that is applied externally on the molecular units that make up the solid matter, while strain is defined as the deformity stress produces on the object on which the force is applied. This stress can be either proportional when the stress applied is relatively small, as in pressing a finger into putty, or disproportional, like the force of a wind storm on a tree.
Force in and of itself cannot be seen, but the result of applied force can be observed. There are two categories of force. Contact force is when objects can be perceived as physically coming in contact with each other and includes frictional force, spring force, tension force, applied force, and air-resistance force. Action-at-a-distance force occurs when objects are not physically touching each other but are affected by each other through pushing or pulling. An example would be the gravitational forces on Earth. Other examples of action-at-a-distance force include electrical force and magnetic force.
Bibliography
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