Need some true and false help.
1.Acceleration in space has tangential, normal and binormal components.
2.Consider a space curve defined by a smooth vector function r(t). If r′′(t)=0 for all t, then the curve is a straight line.
3.Consider a space curve defined by a smooth vector function r(t). If the curve is a straight line, then r′′(t)=0 for all t
4.If a smooth space curve has constant curvature, then it is a circle.

Question

Need some true and false help.
1.Acceleration in space has tangential, normal and binormal components.
2.Consider a space curve defined by a smooth vector function r(t). If r′′(t)=0 for all t, then the curve is a straight line. 
3.Consider a space curve defined by a smooth vector function r(t). If the curve is a straight line, then r′′(t)=0 for all t
4.If a smooth space curve has constant curvature, then it is a circle.

anonymous · Answer

I assume 1 is FALSE because acceleration in space usually defined with both tangential and normal components.

2. & 3. are my real problems

4. Would be False due to the fact that constant curvature could be a circle or line.

anonymous · Answer

Never mind solved it , simply 3 was also false (y)

thomas5267 · Answer

I don't know much about tangential, normal and binormal vectors but won't they form a orthonormal basis in R3 so acceleration can be resolved in such 3 components?