A frame of reference is essentially a set of coordinate axes used to define an object’s position in two- or three-dimensional space. It can also be defined as a set of coordinates used to record the position and time of events. There are two types of frames of reference: inertial frame of reference and non-inertial frame of references.
Let’s focus on the first: inertial frame of reference. An inertial frame of reference is a frame of reference where Newton’s law holds true. This means that if no external force acts on a body, it will stay at rest if it was originally at rest, or it will continue moving at a constant velocity if it was already in motion.
A good real-life example of an inertial frame of reference is a moving truck. When the truck travels at a constant speed, it provides a steady frame of reference for the people inside.
Inertial Frames of Reference Examples
- 1. Train Moving At Constant Speed
- 3. A Floating Raft on Still Water
- 3. An Ice Skater Gliding on a Smooth Rink
- 4. Airplane in Level Flight
- 5. A Moving Walkway at the Airport
- 6. A Bicycle Coasting Down a Gentle Hill
- 7. A Skateboard Rolling on a Flat Sidewalk
- 8. A Spacecraft Gliding Through Space
- 9. Motionless Ramp
- 10. A Garden Bench On A Calm Day
1. Train Moving At Constant Speed
Just like the truck example, a train moving at a constant speed on a straight track is another perfect example of an inertial frame of reference. When you’re inside the train, you can toss a snack to your friend and it will travel through the air just as it would at home. Because the train isn’t speeding up or turning, it provides a steady, inertial frame.
3. A Floating Raft on Still Water
A raft that drifts gently but steadily across still water is also a god example of inertial frame of reference. If you toss a pebble in the air, it comes back to your hand. The raft isn’t jerking or racing, so it’s a peaceful inertial frame.
3. An Ice Skater Gliding on a Smooth Rink
If you love ice skating like I do (I’ve been hooked since I was a kid), this example will feel familiar. Picture yourself giving a good push and then gliding across the ice, smooth and steady. As you keep that gentle slide, it feels like nothing around you is changing speed. That easy glide is exactly what an inertial frame is all about.
4. Airplane in Level Flight
When you’re on a plane cruising at a steady speed, you can stroll down the aisle without feeling like the plane is rushing or stopping. Inside, it feels just like walking in a quiet room on the ground, even though you’re flying miles above the earth.
5. A Moving Walkway at the Airport
Moving walkways make it easier for travelers to get where they’re going quickly and keep foot traffic flowing smoothly. They’re also great examples of inertial frames of reference. As long as the walkway glides at a steady speed, you can stand or walk on it and feel just as steady as if you were on solid ground. The walkway is like a slow, steady “magic carpet” inertial frame.
6. A Bicycle Coasting Down a Gentle Hill
Imagine riding your bike downhill and then letting go of the pedals while it rolls at the same speed. If the hill is gentle and you’re not braking, everything feels smooth and steady—perfect for an inertial frame.
7. A Skateboard Rolling on a Flat Sidewalk
Like the riding a bike downhill example above, picture pushing your skateboard and then letting it roll at a steady pace on smooth pavement. As long as you’re not speeding up or slowing down, it feels calm and balanced, just like an inertial frame.
8. A Spacecraft Gliding Through Space
Imagine astronauts floating in a spaceship that moves steadily through the dark sky. There’s no rushing or braking, so inside they can toss objects and watch them float straight. Space gives another great inertial frame of reference.
9. Motionless Ramp
A motionless ramp is a simple but a good example of an inertial frame of reference. Because the ramp isn’t moving or speeding up, any ball or object placed on it will roll smoothly down only because of gravity, not because the ramp itself is pushing or pulling. It provides a calm, steady background to observe motion.
10. A Garden Bench On A Calm Day
The last example is something many people don’t stop to think about: your garden or lawn bench. When you’re sitting on it on a calm day with no wind, nothing around you is speeding up or slowing down. If you drop a ball, it falls straight down, and that bench becomes your steady “no-acceleration” spot—an inertial frame of reference.