Hi Guys, I was highly studied the Newton's law once again. Probably to recall the concept from the past of my education. Anyway I find out the exercise during solving the friction problems from Hibbeler book. The exercises is state as : The fork lift has a weight W1 and center of gravity at G. If the rear wheels are powered, whereas the front wheels are free to roll, determine the maximum number of crates, each of weight W2 that the fork lift can push forward. The coefficient of static friction between the wheels and the ground is μ s and between each crate and the ground is μ 's. The whole system looks like this: And then it's seperate on two objects: FBD of the 1: FBD of 2: And there is nothing suprised about that except the action and reaction force from the crates and front wheel. I expected that those force will be equal like the 3rd Newton law said. But during the solving and after see those images from book solution looks like 3rd Newton law doesn't work anymore.... Could someone explain what is the reason of that? And where is actually the action and reaction force? I'm confused here.