### Frame Of Reference Motion In A Straight Line Uniform

**Frames of Reference**

**An object’s motion**is described relative to a frame of reference. (Imagine yourself describing the motion of a car to someone standing on the sidewalk; you’d use the sidewalk as your frame of reference.)**A frame of reference**is a set of objects that are fixed in space. (The sidewalk, the trees, the buildings all make up a fixed frame of reference for the car.)**The most common frame of reference**is the Earth. (We tend to think of ourselves as stationary and describe everything else’s motion relative to us.)**Other frames of reference**include the sun, the moon, and the stars. (When describing the motion of a spacecraft, for example, we might use the sun as our frame of reference.)

**Motion in a Straight Line**

**Motion in a straight line**is one-dimensional motion. (Imagine a car moving down a straight road; its motion can be described entirely by its position along the road.)**The displacement of an object**is the distance between its initial and final positions. (If a car starts at point A and ends at point B, its displacement is the distance between A and B.)**The velocity of an object**is the rate at which its displacement changes. (If a car travels 100 miles in 2 hours, its average velocity is 50 miles per hour.)**The acceleration of an object**is the rate at which its velocity changes. (If a car starts from rest and reaches a speed of 60 miles per hour in 10 seconds, its acceleration is 6 miles per hour per second.)

**Uniform Motion**

**Uniform motion**is motion with constant velocity. (A car driving at a steady 50 miles per hour is in uniform motion.)**The acceleration of an object**in uniform motion is zero. (If a car’s velocity is constant, its acceleration is zero.)**The displacement of an object**in uniform motion is equal to the product of its velocity and the time interval. (If a car travels at 50 miles per hour for 2 hours, its displacement is 100 miles.)