Two identical plastic cylinders with a density close to that of water. If the first is immersed in hot water, it will initially sink but will then float up to the surface after a short time. If the second one is then put into ice-cold water, it will initially float but will then sink to the bottom. The reason for this is that the density of the plastic changes more than that of the water when it is heated or cooled.
![Density Paradox Set, 1003498 [U45056], Density and Volume](/imagelibrary/U45056/U45056_01_Density-Paradox-Set.jpg)
![Set of 10 Beakers,600 ml, Low Form, 1002872 [U14210], Glassware](/thumblibrary/U14210/U14210_01_140_140_Set-of-10-Beakers-600-ml-Low-Form.jpg)
![Cartesian Diver, 1002867 [U14090], Buoyancy](/thumblibrary/U14090/U14090_01_140_140_Cartesian-Diver.jpg)
![Immersion Block Al 50 cm³, 1002952 [U15036], Buoyancy](/thumblibrary/U15036/U15036_01_140_140_Immersion-Block-Al-50-cm.jpg)
![Immersion Block Al 100 cm³, 1002953 [U15037], Buoyancy](/thumblibrary/U15037/U15037_01_140_140_Immersion-Block-Al-100-cm.jpg)
![Immersion Block Fe 50 cm³, 1002954 [U15038], Buoyancy](/thumblibrary/U15038/U15038_01_140_140_Immersion-Block-Fe-50-cm.jpg)
![Baroscope -
for experiments with the vacuum recipient, 1003169 [U21853], Vacuum](/thumblibrary/U21853/U21853_01_140_140_Baroscope-for-experiments-with-the-vacuum-recipient.jpg)
![Oersted's Device, 1009710 [U29310], Magnetism](/thumblibrary/U29310/U29310_01_140_140_Oersteds-Device.jpg)
![Immersion Block Fe 100 cm³, 1002955 [U15039], Buoyancy](/thumblibrary/U15039/U15039_01_140_140_Immersion-Block-Fe-100-cm.jpg)
![Vacuum Chamber with Hand Pump, 1010126 [U29497], Vacuum](/thumblibrary/U29497/U29497_01_140_140_Vacuum-Chamber-with-Hand-Pump.jpg)
![Set of 4 Pendulum Bobs, 1003230 [U30035], Oscillations](/thumblibrary/U30035/U30035_01_140_140_Set-of-4-Pendulum-Bobs.jpg)
![Liquid Levels, 1003509 [U58020], Pressure](/thumblibrary/U58020/U58020_01_140_140_Liquid-Levels.jpg)
![Set of 3 Cylinders, Equal in Volume, 1000752 [U8403315], Density and Volume](/thumblibrary/U8403315/U8403315_01_140_140_Set-of-3-Cylinders-Equal-in-Volume.jpg)
![Diaphragm with 4 Double Slits of Different Spacings, 1000597 [U14101], Apertures, Diffraction Elements and Filters](/thumblibrary/U14101/U14101_01_140_140_Diaphragm-with-4-Double-Slits-of-Different-Spacings.jpg)
![Diaphragm with 4 Multiple Slits and Gratings, 1000598 [U14102], Apertures, Diffraction Elements and Filters](/thumblibrary/U14102/U14102_01_140_140_Diaphragm-with-4-Multiple-Slits-and-Gratings.jpg)
![Pascal's Law Apparatus -
for the quantitative measurement of ground pressure, 1002957 [U15070], Pressure](/thumblibrary/U15070/U15070_01_140_140_Pascals-Law-Apparatus-for-the-quantitative-measurement-of-ground-pressure.jpg)
![Magnetic field line apparatus, Two-Dimensional, 1003092 [U19560], Magnetic Fields](/thumblibrary/U19560/U19560_01_140_140_Magnetic-field-line-apparatus-Two-Dimensional.jpg)
![Precision Dynamometer 1 N, 1003104 [U20032], Dynamometers](/thumblibrary/U20032/U20032_01_140_140_Precision-Dynamometer-1-N.jpg)
![High-Quality Vacuum Hand Pump, 1012856 [U205001], Vacuum Pumps](/thumblibrary/U205001/U205001_01_140_140_High-Quality-Vacuum-Hand-Pump.jpg)
![Diaphragm with 3 Double Slits of Different Widths, 1000596 [U14100], Apertures, Diffraction Elements and Filters](/thumblibrary/U14100/U14100_01_140_140_Diaphragm-with-3-Double-Slits-of-Different-Widths.jpg)
![Precision Dynamometer 10 N, 1003107 [U20035], Dynamometers](/thumblibrary/U20035/U20035_01_140_140_Precision-Dynamometer-10-N.jpg)
![Free Fall Apparatus -
to determine the gravitational constant g, 1000738 [U8400830], Free Fall](/thumblibrary/U8400830/U8400830_01_140_140_Free-Fall-Apparatus-to-determine-the-gravitational-constant-g.jpg)