Size matters when it comes to speed

How fast should an animal be able to move? And why are the biggest animals, which pack more muscle, not the fastest? That’s what Yale scientist Walter Jetz was wondering, so he and his colleagues looked at hundreds of animal species and have come up with a new theory that successfully puts a speed limit on most species…

  • There is a theoretical maximum speed that is expected to increase with body size,  however, in order to actually get to any speed you need to first accelerate, and larger animals take much longer to do so – much like a truck accelerating to 60mph compared to a motorbike or car.
  • Large bodied animals simply do not have sufficient energy to reach their theoretical maximum speed.
  • The general distribution is a ‘hump-shape’ as shown in the plots below. Maximum speed increases with size until we reach a critical mass beyond which the maximum speed reached starts to decrease.

screen shot 2019-01-24 at 10.59.30

  • Data for over 450 species were included in the study, across land, air and water.
  • The study provides insight into evolutionary trade-offs for different species as they evolve to increase their chances of survival.

You can listen to the full interview with the Naked Scientists here.

Image copyright Dawn Key


Thick and sticky fluids

The fourth puzzle in the new feature from Tom Rocks Maths – check out the question below and send your answers to @tomrocksmaths on TwitterFacebook, Instagram or via the contact form on my website. The answer to the last puzzle can be found here.

Viscosity is a property of a fluid on the molecular scale and is a measure of the strength of the internal friction between fluid particles. What this means in practice is that the thicker and stickier the fluid, the higher its viscosity.

Your task in this week’s puzzle is to order the six fluids below by their viscosity, lowest first. The answer will be posted in 2 weeks along with the next puzzle – good luck!

WARNING: answer below image so scroll slowly to avoid revealing it accidentally.



3. Air 1.81 x 10-5 [Pa s]

2. Water 8.9 x 10-4

1. Blood 3 x 10-3 

6. Honey 2-10 [Pa s]

5. Ketchup 50-100 [Pa s]

4. Peanut butter 250 [Pa s]

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