What is mass?

a measurement of volume
a measurement of density
a measurement of weight
a measurement of matter

When using the scientist method, which step comes last?

Diverging mirrors and lenses always produce images

Does the distance travelled by an oscillating mass between times t=0 and t2 equal the displacement of the particle over the same time period if t2> t/2? hint: consider a sine wave starting at t1=0, then consider a closing wave starting at t1=0, for your explanation.