Reference Frames and Relative Motion - AP Physics 1

Reference frame: Earth's surface. The ground is the stationary reference from which speed is measured.

Velocity changes by the vector difference between the frames. Vector subtraction gives the relative velocity between frames.

The reference frame in which an object is at rest. The frame where the object has zero velocity.

Relative speed = 100 m/s. Add speeds for opposite directions: $60 + 40 = 100$ m/s.

The observer's frame moves with the object. Observer and object share the same velocity.

The reference frame in which an object is at rest. The frame where the object has zero velocity.

They move together at the same speed and direction. No relative motion means identical velocity vectors.

Perceived forces not due to physical interactions. Acceleration creates apparent forces not from real interactions.

Relative velocity = 20 m/s east. Subtract car velocity from train velocity: $30 - 10 = 20$ m/s.

The platform is an inertial frame. No acceleration means it's an inertial reference frame.

Observed motion appears non-uniform. Acceleration creates fictitious forces in the observer's frame.

Inertial frames have no acceleration; non-inertial frames do. Acceleration distinguishes non-inertial from inertial frames.

Relative velocity = 40 m/s. Add speeds for opposite directions: $25 + 15 = 40$ m/s.

Relative velocity = 15 m/s. Subtract velocities in same direction: $20 - 5 = 15$ m/s.

The sum of their speeds. Add speeds when objects approach each other.

Use vector addition or subtraction. Vector operations account for direction in relative motion.

Velocity = 13 m/s downstream. Add velocities when moving in the same direction: $8 + 5 = 13$ m/s.

Transformation relating measurements in inertial frames. It converts coordinates between frames moving at constant velocity.

The frame in which the observer is stationary. The observer defines their own frame as the rest frame.

$v_{AB} = v_A - v_B$. Subtract object B's velocity from object A's velocity.

Motion is relative to the observer's reference frame. All motion measurements depend on the chosen reference frame.

A reference frame is a perspective from which motion is observed. It's the coordinate system from which we measure positions and motions.

Inertial frames have no acceleration; non-inertial frames do. Acceleration distinguishes non-inertial from inertial frames.

Velocity is relative and changes with the frame. Changing frames changes the measured velocity value.

It appears curved due to fictitious forces. Rotation creates apparent forces like centrifugal force.

Non-inertial frames. Acceleration creates fictitious forces in these frames.

They may observe different velocities for the same object. Relative motion causes different velocity measurements.

$v' = v + u$. Add the frame velocity $u$ to the object velocity $v$.

Speed is frame-dependent and can vary between frames. Different frames measure different speeds for the same object.