Question

Imagine yourself seated on a wheeled desk chair at your desk. Consider friction forces between the chair and the floor to be negligible. However, the friction forces between the desk and the floor are not negligible. When sitting at rest, you push horizontally against the desk, and the chair rolls backward away from the desk. (a) Which force was responsible for your acceleration. (b) What is the reaction force to the force that caused your acceleration? (c)Explain why the desk did not accelerate. Does this violate Newton’s third law? Explain.

Answer 1

(a) The desk pushing against your hand
(b) Your hand, pushing the desk.
(c) The force applied to the desk was less than the amount necessary to overcome static friction. The desk is heavy and has a high static friction coefficient where the legs touch the floor.
Newton's law is not violated. The desk does not move because the force applied to it by the hand equals the static friction force at the floor. The chair moves because it has wheels and low friction, less than the applied force.

Answer 2

Thank you very much