Which of the following events does not involve a change in angular momentum?
1. A spinning ice skater drawing in her arms to increase her rotational speed.
2. A child walking along the perimeter of a merry-go-round as it rotates.
3. A child walking towards the center of a spinning merry-go-round.
4. A ball rolling down a ramp without slipping.
5. A hockey puck sliding without friction on the surface of an icy pond.