Opening a Curtain

Wow! Physics certainly is in everything we do. I say this because opening a curtain is one of those things that we do everyday without thinking about how or why we are able to do it.

In fact, opening a mini-blind has a lot to do with physics. First, the curtain is set on a pulley that allows a person to open the blind from the ground and with less force than

would be required without the pulley. This pulley shows the physics concepts of tension and Newton's second law, net force equals mass times acceleration. In order to open the curtain a

person must apply force to their side of the pulley that is greater than the downward force

of the mass times gravity (weight) of the mini-blind. The force creates tension on the rope and because the rope is the same in the handle and the rest of the curtain the tension transfers to the curtain and as soon as the force becomes more than the weight, the curtain will begin to accelerate upwards.

Because curtains have a large surface area, the rope that serves as a handle on one side of the pulley must be evenly distributed throughout the curtain. This explains the web of string

you see in a curtain as the evenly distributed string

allows the upward acceleration due to tension to be supplied

throughout

the curtain, thus making both sides accelerate upwards at the same time.