If F ⃗ \vec{F} F acts at position vector r ⃗ \vec{r} r , with torque τ ⃗ \vec{ au} τ about the origin, which relations are always correct?

Question

If F ⃗ \vec{F} F acts at position vector r ⃗ \vec{r} r , with torque τ ⃗ \vec{	au} τ about the origin, which relations are always correct?

G1 Physics · Accepted Answer

Step 1: Torque τ=r×F is perpendicular to both vectors in the cross product. Step 2: therefore r·τ=0 and F·τ=0. Final answer: C — r·τ=0 and F·τ=0.

If F ⃗ \vec{F} F acts at position vector r ⃗ \vec{r} r , with torque τ ⃗ \vec{\tau} τ about the origin, which relations are always correct?