Physics can be difficult to learn, but this blog aims to help you get into physics by connecting your GCSE physics lessons with things you see in the world around you.

## Wednesday, 4 May 2011

### Why it’s so hard to get out of bed

“Get up!” comes the cry “You’re missing the best part of the day!” All too frequently, weekend lie-ins are curtailed by inconvenient plans or just one of those eager ‘morning’ people wanting to do something. You groan, you shout back, you may even whimper in extreme circumstances, but “I need to sleep” often doesn’t cut it as a reason for staying in bed.

Well, never fear, help is at hand. Thanks to the marvellous world of Physics there’s now a new reason why it’s so hard to get out of bed (or off the sofa for that matter…). Related directly to Father of Physics Newton himself, inertia is your reason. Inertia is part of Newton’s First Law which states that:

“A body continues in a state of rest or uniform motion unless acted upon by an external force”

So, if we think about the forces that are already acting on you in bed, there is gravity, pushing you down into the mattress, and the force of the mattress pushing against this force to stop you falling through. These are balanced and you are at rest. And in my opinion that’s quite enough forces thankyou, at least until I’ve had my sleep.

Let’s look at getting up then. To overcome this inertia, this resistance to change, we need another force. On some unlucky days this might be in the form of a sibling pushing you out of bed, resulting in a rude awakening, but on most days this will have to come from you. This is where Newton’s Second Law comes in:

“A body will accelerate when an uneven force is applied”

Which normally comes in the pocket-sized Force = mass x acceleration format, a very useful equation all round. So, we have to overcome our inertia to get out of bed by applying a force. But how large? Is it small and insignificant, or is it quite an effort. Well, luckily our bodies are made to move, but actually it’s a pretty large figure.

Ok, so you can see the obvious flaw in my argument, that we were made to move our own bodies about and it not seem like a huge effort. But I’m pretty convinced that morning inertia has some sort of magical property to it! And when all’s said, done and calculated, you’ve at least got a great excuse for demanding breakfast in bed. After all, you’ve got a whole body to move! And of course you can nap in the meantime.