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Forces on a block on a ramp
Age 15 physics
A block resting on a slope is pulled straight down by gravity, while the ramp pushes back at a right angle to its surface and friction grips along the surface. Because the surface is tilted, the block's weight splits into one part pressing into the ramp and one part pulling it down the slope.
Step by step
- The red cube on the slope: the object whose weight the ramp splits into two directions.
- The black arrow pointing straight down: the weight of the cube, always vertical no matter how steep the ramp is.
- The blue arrow at a right angle to the surface: the normal force, the ramp pushing back on the cube.
- The green arrow along the slope: friction, acting up the slope against the cube's tendency to slide.
- The brass arc in the corner: the slope angle, which decides how the weight is shared between the two directions.
Examples
- A skateboard left on a sloping driveway starts rolling once the pull down the slope beats the friction in its wheels.
- Pushing a heavy box up the loading ramp of a moving van feels hard because part of the box's weight pulls it back down.
Key takeaways
- Weight splits into a part pressing into the surface and a part pulling down the slope.
- A steeper ramp means a smaller normal force and a bigger down-slope pull, so sliding starts sooner.
A quiz goes with this lesson
Three questions asked a few days later, to check the idea stuck — not that the picture was seen. In the app, with a subscription.