What is the force that opposes motion and can be found anytime two surfaces are in contact? friction momentum net force spring forces

Karen is running forward at a speed of 9 m/s. she tosses her sweaty headband backward at a speed of 20 m/s. the speed of the headband, to the nearest whole number relative to a stationary observer watching karen

What is the weight of a 8-kg substance in n, kn, kg·m/s2, kgf, lbm·ft/s2, and lbf?

The three classes of rocks are sedimentary, metamorphic, and igneous. how are rocks classified into one of these three groups?