Does a bug hitting your windshield slow down your truck?

[zuz]

Does a bug hitting your windshield slow down your truck?

 

[Greg Bernhardt]

Does a bug hitting your windshield slow down your truck?

Seems like resistance to me. It would be fun if we could calculate the resistance on a truck from a set of common bugs to hit.

 

[Mark44]

Does a bug hitting your windshield slow down your truck?

What do you think?

 

[Bystander]

Does a bug hitting your windshield slow down your truck?

Cue the Men in Black.

 

[Orodruin]

Yes. But not noticeably.

Consider a truck of mass $M$ going at velocity $v$ and a stationary bug of mass $m$. By momentum conservation (and assuming a … fully inelastic… collision)
$$
Mv = (M+m)u \quad \Longrightarrow \quad
u = \frac{M}{M+m}v \simeq v - \frac mM v
$$
where the approximation holds as long as $m \ll M$.

For a 44 tonne truck travelling at 100 km/h and a 2.5 mg mosquito, the slowdown would be about $10^{-9}$ m/s.

 

[Baluncore]

Welcome to PF.

Does a bug hitting your windshield slow down your truck?

Not if you are parked at the time.

When you run into a bug or a raindrop, the mass must be accelerated to the speed of your truck. The energy required will come from your kinetic energy, so your truck will slow down until the engine can replace it, with chemical energy from the fuel or battery.

 

[Orodruin]

The energy required will come from your kinetic energy

This is somewhat misleading. Collisions with bugs or raindrops will typically not be elastic so mechanical energy will not be conserved. Yes, the energy will come from the truck - but the truck will typically lose more energy than that.

It is more relevant to refer to momentum, which is conserved in the collision.