ROTATIONAL MOTION

Why does a circus acrobat spin faster when they pull their limbs close to the body?

• Friction decreases with body size
• Air resistance becomes negligible
• Muscular force increases angular speed
• Moment of inertia decreases, increasing angular speed to conserve angular momentum

What principle explains why a person spinning on a chair slows down when they stretch their arms?

• Conservation of energy
• Newton's third law
• Linear momentum conservation
• Conservation of angular momentum

What happens to the angular momentum of a system when no external torque acts on it?

• It gradually decreases
• It increases
• It changes direction randomly
• It remains constant

Why do internal forces not contribute to the net torque on a system of particles?

• Internal forces are too weak to create torque
• Internal forces act at the center of mass
• Internal forces do not produce any motion
• Internal forces act along the line joining the particles and their torques cancel out

How is torque on a system of particles about the origin defined?

• τ = Σ (r_i · F_i)
• τ = Σ (F_i × r_i)
• τ = Σ (r_i + F_i)
• τ = Σ (r_i × F_i)