Question

1. in space, a spacecraft can keep moving for years without its engines firing.

a) why doesnt it stop?
b) what could eventually change its motion?

part d - critical thinking

1. imagine you are playing hockey on ice. why does the puck glide much farther on ice than on grass?

1. a magician pulls a tablecloth out from under dishes without moving them. explain this works using newtons first law.

Explanation:

8a.

In space, there is no air - resistance or significant external forces to stop the spacecraft. According to Newton's first law (law of inertia), an object in motion will stay in motion with a constant velocity unless acted upon by an external force. Since there is almost no external force in space, the spacecraft keeps moving.

8b.

Gravitational forces from nearby celestial bodies like planets, stars, or even small asteroids or space debris collisions could eventually change its motion. Gravitational forces can attract the spacecraft and alter its trajectory, and collisions with debris can impart an impulse to change its velocity.

9.

The ice surface is much smoother than the grass surface. Friction is a force that opposes motion. On grass, there are more irregularities that create a higher frictional force on the puck, which quickly slows it down. On ice, the lower frictional force allows the puck to glide much farther.

10.

Newton's first law states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. The dishes are initially at rest. When the magician quickly pulls the table - cloth, the friction between the table - cloth and the dishes is not enough to accelerate the dishes significantly in that short time. So, the dishes remain at rest due to their inertia.

Answer:

8a.

There is almost no external force in space, so according to Newton's first law, it keeps moving.

8b.

Gravitational forces from celestial bodies or collisions with space debris.

9.

Ice has lower friction than grass.

10.

The dishes remain at rest due to inertia as the friction from the table - cloth pull is not enough to move them significantly quickly.