The hammer-and-ruler trick

An unusual way to balance a hammer

Your at­ten­tion, please! May we present to you a case of im­pos­si­ble – at first glance – equi­lib­ri­um :)

Safe­ty pre­cau­tions



  • ruler;
  • rub­ber bands;
  • ham­mers.

Step-by-step in­struc­tions

Wrap two rub­ber bands around the han­dle of a ham­mer, form­ing a loop close to its head. Hook the loop around the end of a ruler and set the ruler on the brink of a hor­i­zon­tal sur­face. The ham­mer’s han­dle push­es up­wards on one end of the ruler, while the ham­mer as a whole si­mul­ta­ne­ous­ly pulls the ruler down­wards. The sys­tem bal­ances! You can also re­place the ruler with an­oth­er ham­mer – this will work too!

Process de­scrip­tion

Since the ham­mer and ruler form a con­nect­ed sys­tem, their joint move­ment is de­ter­mined by the po­si­tion of the cen­ter of mass of this sys­tem. As the ham­mer’s head is the heav­i­est el­e­ment in the whole struc­ture, we can as­sume, al­low­ing for a slight in­ac­cu­ra­cy, that the sys­tem’s cen­ter of mass is lo­cat­ed there. Since its cen­ter of mass is lo­cat­ed just be­low the ful­crum, the struc­ture will bal­ance. More­over, this equi­lib­ri­um is sta­ble – if the sys­tem is forced to de­vi­ate from its po­si­tion of equi­lib­ri­um, it will re­bal­ance it­self. And if the con­struc­tion is nudged, it will os­cil­late light­ly.