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Sudden confusion about forces?
When we say W= F*d, is F a force acting throughout the whole distance travelled, or an initial force which causes the whole distance travelled?
Also, when a closed system containing only body A is subjected to some force F to the right, where does the reaction force emerge in the situation, due to Newton's Third Law?
1 Answer
- Anonymous6 years ago
1) The equation W = F*d applies only for a constant force. Your first thought is correct; F is the force being applied as the object travels distance d.
2) Remember that all forces have to have a "cause" or a "source." If force F comes from a man pushing on A, then the reaction force would be A pushing back on the man. If force F is the Earth's gravitational pull on A, then the reaction force would be A's gravitational pull on the Earth.*
*Edited thanks to E's comment. The force of A on the Earth is exactly the same as the force of the Earth on A; only the acceleration is tiny.