# From G. H. Darwin [*c.* 16 October 1873?]^{1}

Dear Father,

If the impact of a weight falling on a horizontal plane is unity—the following table will give it for the other inclinations^{2}

Inclination of plane to horizon | Impact |

0^{o}. |
1^{.} |

10^{o} ^{.} |
9848 = $\frac{9}{10}$ or $\frac{98}{100}$ |

20^{o} ^{.} |
9397 = $\frac{9}{10}$ or $\frac{94}{100}$ |

30^{o} ^{.} |
8660 = $\frac{9}{10}$ or $\frac{87}{100}$ |

40^{o} ^{.} |
7660 = $\frac{8}{10}$ or $\frac{76}{100}$ or $\frac{3}{4}$ |

45^{o} ^{.} |
7071 = $\frac{7}{10}$ or $\frac{71}{100}$ |

50^{o} ^{.} |
6428 = $\frac{6}{10}$ or $\frac{64}{100}$ or $\frac{2}{3}$ |

60^{o} ^{.} |
5000 = $\frac{5}{10}$ or $\frac{50}{100}$ or $\frac{1}{2}$ |

70^{o} ^{.} |
3420 = $\frac{3}{10}$ or $\frac{34}{100}$ or $\frac{1}{3}$ |

80^{o} ^{.} |
1736 = $\frac{2}{10}$ or $\frac{17}{100}$ or $\frac{1}{6}$ |

90^{o} |
0 |

This may be epitomised thus, less to 40^{o} the impact is about $\frac{9}{10}$ at 40^{o} it is $\frac{3}{4}$, 45^{o} it is $\frac{7}{10}$, at 50^{o} = $\frac{2}{3}$, at 60^{o} = $\frac{1}{2}$, at 70^{o} = $\frac{1}{3}$ at 80^{o} = $\frac{1}{6}$ & at 90^{o} of course 0^{o}

Your affectionate Son | G H Darwin

## Footnotes

## Summary

Sends table showing relative force of impact of weight dropped on a plane inclined at different angles.

## Letter details

- Letter no.
- DCP-LETT-9078
- From
- George Howard Darwin
- To
- Charles Robert Darwin
- Sent from
- unstated
- Source of text
- DAR 162: 62
- Physical description
- 2pp

## Please cite as

Darwin Correspondence Project, “Letter no. 9078,” accessed on 25 September 2021, https://www.darwinproject.ac.uk/letter/DCP-LETT-9078.xml

Also published in *The Correspondence of Charles Darwin*, vol. 21