If your lawnmower is a 2 stroke mixing oil in the gas is what it needs to run right. If your lawnmower is a 4 stroke mixing oil in the gas fouls the plug and makes it not run.
You get engine damage from lack of lubrication
generally in a lawnmower you use straight gas. there should be oil in the crankcase for engine lubrication. check the owners manual for proper oil weight
If the lawnmower has two compartments one for gas and the other for the oil, then put gas in the gas and a 30w type oil in the oil compartment. Simple as that. If you have an engine with only one compartment then you'll need to check on the manufacturers suggestions which is usually 40:1 or something close.
it is gas only no oil is added to the gas
Yes definitely! Do Not Run it!! If there is no oil in your fuel it will seize the engine. Because the oil in your gas is the only oil that lubricates your motor.
No, normally weedeater gas has oil mixed in with it. This will gunk up the engine and cause the spark plug to fail.
You can cut down trees with your lawnmower. Warning: Do not actually try to cut down a tree with your lawnmower. More than likely, the gas in the chainsaw is mixed with 2-cycle oil. If your mower also has a 2-cycle engine, nothing will happen. If your mower has a 4-cycle engine, the engine will probably smoke (bluish in color) until the oil is burnt up during combustion. At worst, the oil in the 2-cycle oil/gas mixture will foul up the spark plug and you will probably have to clean it pretty often until the oil is burnt up.
to put the oil in the lawnmower's crankcase would be fine, so long as it is an appropriate viscosity.
Anything other than the required fluids needed to run an engine (gas, oil, coolant) can seriously damage any engine.
sugar
Drain the oil and gas out of the crankcase and put oil back it should be OK