Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first Which pulls more, the apple or the orange? They both exert the same force on each other but in opposite directions. The orange (on the cart) will accelerate towards the apple because the force of friction that resists the pull is so low. Note that as well as any unbalanced forces acting on each object the acceleration of each object will depend on the inertia (mass) of each in accordance with a = F NET /m

A truck driving down the road runs into a bug flying the other way. a) Which object has the greater force exerted on it? b) Which object will change its motion the most? F TB F BT Both objects have the same small force exerted on them during the collision according to Newton’s third law. The bug squishes easily! The bug obviously changes its motion significantly more than the truck because of its much lower inertia (mass). Truck : a T = F / M Bug : - a T = - F / M

The moon moves around the earth. a) Which object has the greater force exerted on it? b) Which object will change its motion the most? Both objects have the same large force exerted on them during the collision according to Newton’s third law. The Moon obviously changes its motion significantly more than the Earth because of its much lower inertia (mass). Earth : a E = F / M Moon : - a M = - F / M F ME F EM

A boxer hits a piece of paper. a) Which object has the greater force exerted on it? b) Which object will change its motion the most? Both objects have the same small force exerted on them during the collision according to Newton’s third law. The paper obviously changes its motion significantly more than the glove because of its much lower inertia (mass). Glove : a G = F / M Paper : - a P = - F / M F GP F PG

A bullet is fired from a gun. a) Which object has the greater force exerted on it? b) Which object will change its motion the most? Both objects have the same force exerted on them during the collision according to Newton’s third law. The bullet obviously changes its motion significantly more than the gun because of its much lower inertia (mass). Gun : a G = F / M Bullet : - a B = - F / M F BG F GB