Textbook

Forces

If you place a book in the palm of your hand and raise your hand over your head, you have applied a force to that book. You "lifted" that book up.

If you and a friend play "tug-of-war" or arm wrestle, each of you are pulling or pushing, trying to win the game. Who will win? The person that can apply the most force.

What if you played "tug-of-war" with three small people pulling against two large people? The group that pulls with the most force will win.

If you get pulled or pushed in many directions which way will you move? For example, let's say that you are walking into a strong wind and a friend grabs your hand and tries to pull you to one side. Which way will you go, forward, backward or to the side? To find out you have to add all of these forces together.

How does this apply to flight? Forces act on the vehicle or projectile at the same time. Which way the object will go depends on the strength of each of these forces. Scientists and engineers have developed methods to determine these forces and predict which way an object like an airplane or a ball will go.

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