Force Quit:
Force Quit is similar to End Task in Task Manager (Ctrl + Alt + Delete) on Windows
- Open the Force Quit Applications menu
- Either press these three keys together: Option, Command, and Esc
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- Or choose Force Quit from the Apple menu in the upper-left corner of your screen.
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- Select the app that's causing problems (which may say not responding next to it)
- Click Force Quit at the bottom
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Activity Monitor:
Activity Monitor is similar to more details version of Task Manager on Windows
- Open Activity Monitor
- Either go to Applications > Utilities > Activity Monitor
- Or press Command+Spacebar and type "activity monitor", then select it from the results list
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If you select a process you can inspect its details (View > Inspect Process or Command+I) or kill it (View > Quit Process or Option+Command+Q). Since this displays system processes, be careful not to kill a process unless you're certain that doing so won't cause system problems.
Learn more about Activity Monitor's capabilities from Apple's Support page: https://support.apple.com/en-us/HT201464