How do geckos defy gravity

Lines 2-4
Geckos seem to defy gravity, scaling vertical surfaces and walking upside down without claws, adhesive

glues or super-powered spiderwebs.

• Geckos love spiders, because they have super powers

• Geckos can climb vertical surfaces, because they have claws

• Geckos can go up and down on a vertical surface even if they do not have claws

• None of the above

Lines 4-5
Instead, they take advantage of a simple principle: that positive and negative charges attract.

• Positive charges are more attractive than negative charges

• Negative charges are more attractive than positive charges

• None of the above

Lines 5-6
That attraction binds together compounds, like table salt, which is made of positively charged sodium ions

stuck to negatively charged chloride ions.

• Table salt is composed of sodium and chloride

• Sodium ions are positively charged

• Chloride ions are positively charged

• Chloride ions and Sodium ions are attracted because of their respective charge

• None of the above

Lines 6-7
But a gecko's feet aren't charged and neither are the surfaces they're walking on. So, what makes them

stick?

• Geckos have charged feet

• Geckos feet stick

• Geckos feet are not charged

• The surface the Geckos walk on are charged

• The surface the Geckos walk on are not charged

Lines 9-11
Elements like oxygen and fluorine really, really want electrons, while elements like hydrogen and lithium

don't attract them as strongly. An atom's relative greed for electrons is called its electronegativity

• Electronegativity is the measure of an atom’s need of electrons

• Electronegativity is the measure of an atom’s negativity

• Hydrogen and Lithium have a higher electronegativity than Oxygen and Fluorine

• Hydrogen and Lithium have a lower electronegativity than Oxygen and Fluorine

• All of the above

Lines 14-17
That creates a thin spot in the electron cloud where positive charge from the atomic nuclei shines through,

as well as a negatively charged lump of electrons somewhere else. So the molecule itself isn't charged, but

it does have positively and negatively charged patches

• There are positively charged areas on a molecule, even if it is not charged

• There are negatively charged areas on a molecule, even if it is not charged

• All of the above

Lines 25-27

That's the gecko's secret. Gecko toes are padded with flexible ridges. Those ridges are covered in tiny hair-

like structures, much thinner than a human hair, called setae. And each of the setae is covered in even tinier

bristles called spatulae.

• Geckos have flexible toes with ridges

• Geckos have toes with flexible ridges

• The ridges are covered in setea, covered with spatula

• Geckos have padded feet

• all of the above

Lines 28-31

When the gecko unfurls its flexible toes onto the ceiling, the spatulae hit at the perfect angle for the van der

Waals force to engage. The spatulae flatten, creating lots of surface area for their positively and negatively

charged patches to find complimentary patches on the ceiling

• The spatula stick to the ceiling because of the Van Der Waals force

• The surface area is also important

• The surface area has nothing to do with it

• All of the above

Lines 31-33

Each spatula only contributes a minuscule amount of that van der Waals stickiness. But a gecko has about

two billion of them, creating enough combined force to support its weight. In fact, the whole gecko could

dangle from a single one of its toes.

• Each spatulae is minuscule but it sticks

• Each spatulae contributes a little, but there are a lot of them

• The combined force of all the spatulae contributes to the adhesive capacity of the Geckos

• A Gecko can hold to a surface by only one toe

Lines 25-27

That super stickiness can be broken, though, by changing the angle just a little bit. So, the gecko can peel its

foot back off, scurrying towards a meal or away from a predator.

• It’s not possible for a Gecko to break this super stickiness

• The super stickiness does not depend on the angle

• The Gecko can control the stickiness as he wishes

• Stickiness depends on the angle