Relative Motion

What is Relative?

• Relative means opposite

• Relative means in comparison of something else

What is relative motion?

• Measuring the speed of an object

• Measuring the movement of an object compared to another object (reference point)

• Measuring the movement of an object WITHOUT using reference point

Observers using different ___________________ may measure different velocities for an object in motion

• frame of reference

• relatives of motion

• projectile motions

• constant velocity

A spy runs from the front to the back of an aircraft carrier at a velocity of 3.5 m/s. If the aircraft carrier is moving forward at 18.0 m/s, what is the spy’s speed relative to the plane?

• 21.5 m/s left

• 21.5 m/s right

• 14.5 m/s left

• 14.5 m/s right

A boat is on a river. If the boat is headed due west with a speed of 2.5 m/s and the river’s velocity is 3.0 m/s to the east, what will the boat’s velocity relative to Earth be?

• 5.5 m/s west

• 0.5 m/s west

• 2.5 m/s west

Answer explanation

The question says the reference point is Earth (relative to Earth). The earth is standing still so the boat is moving 2.5 m/s relative to the Earth.

A girl at an airport rolls a ball east at 0.15 m/s on a moving walkway that moves east at 1.50 m/s, what is the velocity of the ball relative to the walkway?

• 1.65 m/s east

• 1.35 m/s east

• 1.65 m/s west

• 1.35 m/s east

Answer explanation

same direction: subtract

A person standing still on the ground sees a train traveling north. What direction is the train traveling relative to the person.

• North

• West

• East

• South

A person standing on a platform viewed from a train traveling north. What is the direction the person is traveling relative to the train?

• North

• West

• East

• South

A ball dropped by a boy walking at a speed of 1 m/s viewed by the boy. What direction is the ball moving relative to the boy?

• West

• South

• Up and down

• Stationary