20 MPH is less than the average days wind speed in parts of the midwest. If YOU don't feel in complete control, then it's not safe. 20mph is normally OK, but what you need to find out is whether there will be higher gusts expected. It is usually the sudden gusts that can catch a driver unawares and make it dangerous.
It also depends on what the temperature is that day. I looked around at people's personal experiences and I came to the conclusion that anything above 40 miles per hour (even if its gusts of wind) is probably too strong of a wind to hike in. If you want to stay safe, stick with anything below 20 to 25 miles per hour.
50-75 mph – At 50+ MPH winds are officially classified as “damaging”.
Gusts are reported when the peak wind speed reaches at least 16 knots (18 mph) and the variation in wind speed between the peaks and the lulls is at least 9 knots (10 mph). The winds of 15-25 mph, with gusts of up to 45 mph, may blow around unsecured objects, take down tree limbs and potentially cause power outages.
"Breezy" to "Windy" conditions. Sustained wind speeds around 20 mph, or frequent gusts of 25 to 30 mph. " No Discernable Threat to Life and Property from High Wind." Note: In "High Wind" conditions, small branches break off trees and loose objects are blown about.
Breezy is described as a sustained wind speed from 15-25 mph. Windy is a sustained wind speed from 20-30 mph. Winds sustained at 74 mph or greater.
Read the six things you need to know about wind warnings for more information about wind warnings....Wind warnings and gusts.Average wind speed (knots)Gust strength that should be planned for (knots)Wind Warning thresholds1521202826 - 3336 - 45Strong wind warning issued34 - 4748 - 65Gale force warning issued
Knots to Miles per hour tableKnotsMiles per hour20 knots23.0221 knots24.1722 knots25.3223 knots26.47
Definitely Spiderman, though he prefers to travel by webs he can easily catch up to a speeding car even outrun a cheetah. That's over 70 mph, Caps top speed is no more than 40 mph. Originally Answered: Who would be faster in a foot race, Spider-Man or Captain America? Spidey wins.
His movement is possible, but he would have to lose some height to move long distances, as you mention in the comment. The bottom line is that air resistance would probably overcome any gain in swing amplitude he might get from resonating his body with the swing as children do on a swing.