This activity can help children learn about the effects of wind speed on a windmill. Have the children blow on a pinwheel with breaths of different intensity, and then have them observe how the force of the breath that they exert affects the pinwheel. The children will notice that smaller puffs may barely move the pinwheel, but larger exhales will cause it to spin wildly. Explain to the children that wind creates the movement of a windmill's blades, and that the rate of the movement is dependent on the wind's force and speed.
This activity can help illustrate how the position of a windmill in relation to the wind's direction will also affect the movement of the windmill. Take the pinwheel and secure it to a surface so that the pinwheel is freestanding. Have the children blow on the pinwheel from behind it, in front of it, and from either side of it, using the same force with each breath. Explain to the children that a stationary windmill's blades will rotate faster or slower depending on the direction of the originating wind and the design of the blades.
This activity can help to illustrate the power that a windmill can create. Push a threaded needle through the front center of the pinwheel so the needle sticks out. Attach a small piece of paper to the other end of the thread. Blow on the pinwheel in one direction so that the needle rotates, looping the thread around the head of the needle and pulling the paper up. Explain to the children that the windmill changes the wind's force into its own.