* Physical Change: A change in the form or appearance of a substance, but not its chemical composition.

* Chemical Change: A change where a new substance is formed with different chemical properties.

When you heat tungsten, you are increasing its temperature. This causes the atoms within the tungsten to vibrate faster and emit light (glowing red). The tungsten itself hasn't been transformed into a new substance. It's still tungsten, just at a higher temperature.

Key points:

* The chemical composition of tungsten remains the same.

* The change is reversible. If you cool the tungsten down, it will stop glowing.

Therefore, heating tungsten until it glows red is a physical change.