According to Newton's third law, what other force must be happening?
The wheelchair is pulling on Finn. The wheelchair is pushing on Finn.
Isaac Newton was born in the 1600s and studied how objects move. He discovered three fundamental laws about forces and motion. According to Newton's third law, for every force, there is an equal and opposite force.
Consider the following force:
Finn is pushing on his friend's wheelchair.
According to Newton's third law, for every force, there is an equal and opposite force. This means that if one object is applying a force on a second object, the second object must also be applying a force on the first object, but in the opposite direction.
For example, if your hand is pushing down on a table, the table is also pushing up on your hand. Or, if you are pulling forward on a rope, the rope is also pulling back on you.
Finn is pushing on the wheelchair. So, Newton's third law tells you that the wheelchair is pushing on Finn.