I got a question in the quiz that does an inertial frame be necessarily orthogonal or it could have non-orthogonal axes? I was wondering about the answer but I couldn't think through. Can anybody help me with this?

If a particle is attached to a string and made to move in a vertical circle with initial velocity of $\sqrt{4gl}$ $m/s$ where l is the length of string, at some angle (approx $131°$ with the initial position), the string slacks and the particle leaves the circular path and undergoes projectile mo...

When I pull a cork out of a wine bottle, it usually expands slightly in circumference. This makes sense: you want the cork to be slightly compressed relative to its natural diameter when it's inside the bottle in order to make a tight seal. But I've noticed that the cork usually expands asymmetri...

What's the lifespan of Deuterium and Helium-3 in the sun? How long on average, the Deuterium and Helium-3 atoms last in the Sun's core?