Hcs - Physics Space Summary

HSC PHYSICS: MOTORS AND GENERATORS

1. "Motors use the effect of forces on current-carrying conductors in magnetic fields."

Students learn to "discuss the effect on the magnitude of the force on a current-carrying conductor with several variations of factors."

Mass is the amount of matter in a body whereas weight is the force due to gravity acting on a mass. Mass will not change where the acceleration due to gravity is different but the weight will change.       

For example, bathroom weights are calibrated in kg, but actually measure weight as they work by the mass on them compressing the spring. Therefore, it takes into account Earth's gravitational pull. On the Moon, the gravitational force is about 1/6 that of Earth, so the spring will compress about 1/6 as much. The scales will therefor read 1.6kg instead of 10kg.

W = mg            where W = weight, m = mass, g = acceleration due to gravity.

Astronauts in space appear weightless even though gravity is acting on them. At the height of a typical space station gravity is about a third of its value on Earth. The astronauts appear weightless because they are falling around the Earth with the same acceleration as their space station. You could get the same situation on Earth if you were in a lift when the cable broke.

True weight is equal to mg for whatever value g has at that location. Apparent weight is equal to the reaction force exerted on the object and is equal to mg + ma where ‘a' is the upward acceleration of the object. (For an object accelerating down, a is negative)

Students learn to "explain that a change in gravitational potential energy is related to work done."