You see, when someone steps on your foot with the heel of a high heel, it's more painful then someone stepping on your foot with a flat shoe. How do I know this? One of them stepped on my foot last night and it hurt! But physics also explains this.
Pressure is equal to force divided by area. The greater the pressure acting on your foot, the greater the pain is likely to be. The amount of force applied to the foot is the same regardless of which shoe is stepping on you. The gravitational force acting on your body doesn't change, unless you add or lose mass. What changes is the area over which that force is applied.
If you divide the same force by a smaller area, the pressure goes up. For a high heel, only a small area is actually touching the ground, or in last night's case, my foot. That force, spread over a much smaller area, increased the pressure on my foot, causing me to yelp out in pain! So for parents with young daughters out there wearing high heels for the first time, spread this knowledge, for it may one day save the foot of a loved one!!! :-)