Science labs › Physics › Slide and Light Gates
Let a toy sled slide down a slide. How fast does it pick up speed?
Slide and Light Gates lab · Last updated: 16 October 2026
A toy sled slides down a slope past light gates, which time it automatically, just as in a school science lab. You change the steepness and read the speeds. Does the sled speed up by the same amount every second?
What you'll discover
- A sled on a smooth slope gains speed at a steady rate, called acceleration.
- A steeper slope gives a bigger acceleration, up to a straight drop when it is vertical.
- Light gates measure speed by timing how long the sled takes to pass through.
The science in plain words
When the sled sits on a slope, gravity pulls it straight down. Part of that pull acts along the slope, pushing the sled downhill, and part presses it into the surface. The steeper the slope, the bigger the share that pushes it along.
If the slope is smooth, that downhill push stays the same all the way down. A steady push gives a steady acceleration: the sled's speed goes up by the same amount every second. Plot speed against time and you get a straight line, with a steeper line for a steeper slope. On a vertical drop, the acceleration is the full 9.8 metres per second every second of a straight drop.
Friction pushes back up the slope and reduces the acceleration. On a gentle, rough slope the sled may not move at all.
Light gates work by shining a beam across the track. When the sled breaks the beam, a timer starts; when it clears the beam, it stops. Knowing the sled's length and the time, you can work out its speed. Galileo used ramps in a similar way four centuries ago, slowing down falling motion so he could measure it.
Where it fits
- India, NCERT: Class 9 science, Chapter 7: Motion
- United States: Grades 6 to 8
- Next Generation Science Standards: MS-PS2-2
Common questions
Why does something speed up going down a slope?
Part of gravity's pull acts along the slope. That steady push makes the object gain speed at a steady rate, which is called acceleration. Friction reduces it a little.
What is acceleration in simple words?
Acceleration is how quickly speed changes. If a sled's speed goes up by 2 metres per second every second, its acceleration is 2 metres per second squared.
How do light gates measure speed?
A light gate times how long an object blocks a beam of light. Dividing the object's length by that time gives its speed at that point.
Related labs
- Friction Drag Test: Pull a block with a newton meter. How hard do you have to pull on ice, wood or sandpaper?
- Rolling Race: Race a ball, a cylinder, a hoop and a hollow ball down a ramp. Which one wins?
- Projectile Launcher: Aim the launcher and fire a marble. Which angle sends it furthest?
See all physics labs or every Taz science lab.
Try it yourself
The Slide and Light Gates lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.