Forces in Physics: Understanding Weight and Acceleration
How do forces vary when a barbell is accelerated upward?
When an athlete holds the barbell directly over his head, the force he exerts on the barbell is the same as the force exerted by the barbell on him. How do these forces (the weight of the barbell, the force exerted by the man on the barbell, and the force exerted by the barbell on the man) vary for the case in which the barbell is accelerated upward?
Explained
When the barbell is at rest above the athlete's head, the athlete exerts a force equal to the weight of the barbell downward. This is a phenomenon governed by Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. The weight of the barbell pulls downwards due to gravity, and the athlete exerts an equal force upwards to balance this and keep the barbell at rest.
Final answer
However, when he accelerates the barbell upwards, he needs to apply a force greater than its weight, according to Newton's second law - force equals mass times acceleration. The athlete must exert a force greater than the weight of the barbell to achieve upward acceleration.
When the barbell is motionless above the athlete's head, the forces are balanced as the athlete exerts a force equal to the weight of the barbell. This demonstrates Newton's third law of motion in action. The barbell exerts a force downward, while the athlete counteracts this force by exerting an equal force upward.
However, when the barbell is accelerated upward, the forces change. In this scenario, the athlete must apply a force greater than the weight of the barbell. This additional force is necessary to overcome the inertia of the barbell and accelerate it upwards. According to Newton's second law (F=ma), force is equal to mass times acceleration. Therefore, to accelerate the barbell upward, the athlete must exert a force that exceeds the weight of the barbell.
In summary, when an athlete accelerates a barbell upward, the forces involved are no longer balanced, and the athlete must exert a greater force than the weight of the barbell to achieve this acceleration. Understanding the relationship between forces, weight, and acceleration is essential in the study of physics and mechanics.