We have seen that part of physics is a study of motion, including accelerations, which are changes in velocities. Physics is also a study of what can cause an object to accelerate. That cause is a force, which is, loosely speaking, a push or pull on the object. The force is said to act on the object to change its velocity. For example, when a dragster accelerates, a force from the track acts on the rear tires to cause the dragster’s acceleration. When a defensive guard knocks down a quarterback, a force from the guard acts on the quarterback to cause the quarterback’s backward acceleration. When a car slams into a telephone pole, a force on the car from the pole causes the car to stop. Science, engineering, legal, and medical journals are filled with articles about forces on objects, including people.
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