solid state chemistry
A piece of glass is scratched with a diamond-tipped stylus, showing that diamond is harder than glass.
A piece of tape pressed against a sample of molybdenum sulfide will peel off layers of the sample. Additional tape can be used to cleave the peeled sample hundreds of times.
A piezoelectric crystal is pressed producing an electric current that lights an attached bulb. While still pressed the electric circuit is broken. Once the circuit is restored and electricity allowed to flow, the stress in the crystal is relieved.