Question

A weightlifter stands on a bathroom scale. He pumps a barbell up and down. What happens to the reading on the scale as he does so? What If? What if he is strong enough to actually throw the barbell upward? How does the reading on the scale vary now?

Short answer

When a weightlifter pumps a barbell up and down, the scale reads the larger upward force that the floor exerts on them together.

Step-by-step solution

 A concept:

If the weightlifter throws the barbell up so that he loses contact with his hands, the reading on the scale will return to normal and read only the weightlifter's weight until the barbell falls back into his hands, at which point the reading will jump. up.

The reading on the scale goes upwards:

The lifter provides an upward force on the barbell as it passes through the bottom of a cycle, and the scale reads the bigger upward force that the floor puts on them both.

The scale reads less than normal near the top of the weight's motion.

If the weightlifter throws the barbell upwards so that it loses contact with his hands, the reading on the scale will return to normal, reading just the weight of the weightlifter, until the barbell lands back in his hand at which time the reading will jump upward.