## Energy in rolling

The wheel is a game changer! Everyone knows that. But exactly why? It turns out to be because wheels don’t expend energy! (At least no…

## The human body “machine”

It’s tough to hold up a backpack. You can’t do that forever – eventually you will fall down under the weight. So, you are doing…

## Equilibrium & stability

Since a stationary point is a point that is momentarily flat, that point is like every point on a flat shelf. Place a ball on…

## Work-energy theorem

In every-day life we often have not too many types of energies involved. Let go of a basketball, and gravity does work on it so…

## Stationary points

On the top of the hill, it is flat. Only momentarily flat, sure, but nevertheless flat. It’s a point where the curvature changes from upwards-pointing…

## Potential well

Place an egg at the top of an upside-down bowl and it will roll down. But make a dent at the top, a small “valley”,…

## Power

Push a box over the floor. It takes effort and requires work being done, meaning energy being spent. Now push it faster over the same…

## Energy conservation vs momentum conservation

Roll a cart off a hillside towards a bridge. Energy conservation can easily tell that the energy stored to begin with, in moment $\unicode{x2460}$, turns…

## Energy conservation (1st law of thermodynamics)

With no fuel (no stored chemical energy) your car won’t start moving. Because, where would the kinetic energy come from? With some kinetic energy, the…

## Sign conventions

Which of these is the correct energy conservation law: $$\unicode{x24b6} \quad E_1+Q+W=E_2\qquad\qquad\unicode{x24b7} \quad E_1-Q+W=E_2$$$$\unicode{x24b8} \quad E_1+Q-W=E_2\qquad\qquad \unicode{x24b9} \quad E_1-Q-W=E_2$$ The answer is… … they all…

## Heat & conservative forces

When rubbing your hands fast, they become… warm? Heat has been generated! Let’s symbolise it $Q$. Slide a box over the floor, or make your…

## Dot-product

Right now we have two versions of the work formula: $W=F_\parallel \Delta s$ and $W=F\,\Delta s_\parallel$, which include the $\parallel$-symbol, possibly some cosines when we…

## Work

You pushed the heavy box several metres over the floor. It took a lot of work! This word ‘work‘ is apparently used in this context…