Weight Lifting

When lifting weights, specifically bench pressing, one must do work on the bar holding the weights. The person has to apply a force upwards in order to lift the weight up. Opposing the force that they are applying is the force of gravity which is going down. The person is doing work on the bar and weights when they lift them up. Work refers to an activity involving a force and movement in the direction of the force. In order for work to be done the person myst use energy. The equation to find the amount of work that the person does is Works= Force • Distance. The force can be found by multiplying gravity of earth (9.81 m/s^2) with the mass of the weight. The distance is going to be close to the length of the persons arm. The person while weight lifting involves Kinetic Energy and Potential Energy. The Kinetic Energy is taking place by lifting and lowering the weight. The Potential Energy is taking place when the weights are at it's maximum distance which is the length of the persons arm. The equation for KE ( Kinetic Energy and PE ( Potential Energy) are PE=m•g•h , KE=(m•v^2)/2. To bring the weights back down to ones chest gravity must take over. The resistance of the persons arm (friction force) slows the momentum of the weight down by controlling the velocity. The equation to find the momentum is p= m•v. The work done by gravity when lowering the bar is equal to the PE where the acceleration is equal to gravity. Without the resistance of ones arm when lowering the weights, the weights would run down onto the persons head or chest resulting in major injuries or even death.