• Precessa – Gyroscopic Precession Physics T-Shirt – white
  • Precessa – Gyroscopic Precession Physics T-Shirt – male model, black
  • Precessa – Gyroscopic Precession Physics T-Shirt – flat lay, black
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PrecessaGyroscopic Precession

Precessa – Gyroscopic Precession Physics T-Shirt

$29.99 USD
$29.99 USD
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Color
White · Black
Size
S–5XL
Made
To order · shipping times

Why doesn’t a spinning top fall over? Gravity pulls down, but the torque it makes points sideways, and torque changes angular momentum in its own direction: τ = dL/dt. So the spin axis swings slowly around a cone instead of toppling. Precessa is that top, pushed down and going sideways. Pixel-art unisex tee; equation, symbols and sources in the physics panel below.

Color
Size

Size guideS–5XL · inches

Details

Size & fitS–5XL

Unisex heavy cotton (Gildan 5000), classic fit.

SizeWidthLengthSleeve
S182815.1
M202916.5
L223018
XL243119.5
2XL263221
3XL283322.4
4XL303423.7
5XL323525

Measurements in inches, ±1.5 in tolerance.

ShippingFree US

Free US shipping · $10 flat shipping outside the US. Printed to order for you.

Delivery times & where we ship

Returns & replacements21 days

Every item is printed to order, so we can’t accept returns or exchanges for change of mind, or if you ordered the wrong size or colour.

Print defect, misprint, damage or the wrong item? We’ll send a free replacement, or a refund if you prefer. Report it within 21 days of delivery with a photo; no need to send it back.

Full refund & replacement policy

The physics

Gravity pulls a tilted top down. It does not fall. It swings sideways around the vertical instead.

Torque changes angular momentum in the direction of the torque, and for a spinning top that direction is sideways. So the spin axis sweeps round in a circle, slower the faster it spins.

Push Precessa down. She goes sideways.

Equations

\[\frac{d\mathbf{L}}{dt} = \boldsymbol{\tau} = \mathbf{r}\times m\mathbf{g}\]
\[\Omega_p = \frac{m g r}{I\,\omega}\]
SymbolMeaningUnit
\(\mathbf{L}\) spin angular momentum of the top \(\mathrm{kg m^2/s}\)
\(\boldsymbol{\tau}\) torque of gravity about the pivot \(\mathrm{N·m}\)
\(\mathbf{r}\) position of the centre of mass from the pivot \(\mathrm{m}\)
\(m\) mass of the top \(\mathrm{kg}\)
\(\mathbf{g}, g\) gravitational acceleration \(\mathrm{m/s^2}\)
\(\Omega_p\) precession rate (fast-spin approximation) \(\mathrm{rad/s}\)
\(I\) moment of inertia about the spin axis \(\mathrm{kg m^2}\)
\(\omega\) spin rate \(\mathrm{rad/s}\)

Sources

  1. Feynman Lectures on Physics Vol. I Ch. 20: Rotation in Space (the gyroscope)
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