Amachine that has no friction to overcome is called

a. ideal machine
b. complex machine
c. real machine
d. smooth machine

Could someone . i have tried to solve myself but my calculation is off

What is the measurement of how fast an object moves relative to a reference point?

I'm thinking it's 2 you are asked to explain the earth's magnetic field. which is the best reply? 1. the earth's magnetic south is similar to the north pole of a magnet. 2. the earth's core has a strong magnetic charge similar to the south pole of a magnet. 3. the earth's geomagnetic south is similar to the south pole of a magnet. 4. the earth's magnetic charge is not centered at either pole; it varies based on location.