\(\def \u#1{\,\mathrm{#1}}\) \(\def \abs#1{\left|#1\right|}\) \(\def \ast{*}\) \(\def \deg{^{\circ}}\) \(\def \tau{\uptau}\) \(\def \ten#1{\times 10^{#1}}\) \(\def \redcancel#1{{\color{red}\cancel{#1}}}\) \(\def \BLUE#1{{\color{blue} #1}}\) \(\def \RED#1{{\color{red} #1}}\) \(\def \PURPLE#1{{\color{purple} #1}}\) \(\def \th#1,#2{#1,\!#2}\) \(\def \lshift#1#2{\underset{\Leftarrow\atop{#2}}#1}}\) \(\def \rshift#1#2{\underset{\Rightarrow\atop{#2}}#1}}\) \(\def \dotspot{{\color{lightgray}{\circ}}}\) \(\def \ccw{\circlearrowleft}\) \(\def \cw{\circlearrowright}\)
Chapter 1: Equilibrium
1.

What are Forces?

Physicists have a habit of taking ordinary words and using them in unusual ways (as we will see with work and power), but a force in physics is just what you think it is: a push or a pull.

Forces are one of the most fundamental concepts of physics. Forces are what hold atoms and solar systems together. They are what make chemistry possible. They are how we interact with the world: how we feel, see, hear, smell, taste, even think.

"Hey, you said it would go faster if we both pushed!"

When describing a force it is important to mention how strong it is and what direction the force is pointing in. If someone asks you to help them push a car up a hill, it makes a difference whether you are pushing from the front or from the back! A force is what we call a vector quantity, but we'll explain what that is later.