Q: why is the new mac book getting heated

Hi. What model Macbook do you have? Why do you think it's running to hot? Do you have any kind of an app to monitor the temp? If so,what reading are you getting? Does this only happen when running multiple apps?  Are you fans running loud? 55 to 65 degree c is not all the hot for a laptop. Here is an app that will tell you what the fan speed is and the temp.

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What model Macbook do you have?

The OP said that he had a, "new macbook 12 inch." They don't have a fan.

Use your Activity Monitor app to identify what processes may be hogging cpu resources. Quit any 3rd party software or plugins that you can identify as using excessive cpu resources.

Apps can affect Mac performance, battery runtime, temperature, and fan activity - Apple Support

A link has been posted in this thread to the "macupdate" website. Do not follow that link, and never download anything from that site. It intentionally distributes OS X malware by packaging some free applications (such as "Firefox" and "Skype") in an unnecessary and malicious "installer."

All software should be downloaded directly from the developer's website or from the App Store. Don't trust any site such as "macupdate" that aggregates links.