Depends on the law, which can be different from one place to another. It's always a good idea though, even if the law doesn't ask for it.
wear helmet, use reflectors when riding at night. always wear bright clothes. always ride WITH the flow of traffic. always walk your bike across a roadway.
Seriously? NO.
That's all down to how hard you're riding. Most people will use more effort when riding IRL than riding stationary bikes.
A bicycle alone only use up space. But a human riding a bicycle will have to use force to get the bicycle to do anything, by pushing on the pedals, pulling on the handlebar ASO.
because it is fun
Yes you can use a motor cross helmet for bmx riding i actually recommend it but that's my opinion
A bicycle and a state ID and a helmet
Wearing a bicycle helmet can greatly decrease the risk of head trauma. Other injuries on bicycles will not be affected by helmet use. The helmet is there to protect the head.
I like riding my bicycle around the house.
If you fall and hit your head on the sidewalk, a helmet will keep you from busting your head open. If you fall of a bike and land on your head, a helmet will protect you head.
There are a great deal of benefits that you can get by wearing a bicycle helmet. One of the most obvious ones is that of safety - if you have a crash, your head is not likely to be injured. You can also use keep your hair dry.
Usually called "wall of death"