Verified answer

Demend is generally more elastic in the long run than in the short run. This is because in the short run,

1 the customer might not know where else to get his purchases, or

2 not know what other substitutes exist, or

3 he might be set in is tastse and this takes a while to change.

Also,

4 the entry of substitues in the market makes the demand for each substitute more elastic.

Often because of the availability of substitutes. Take a recent example. When Amazon introduced its Kindle reader, price elasticity was low. They charged a high price and demand exceeded supply. Within a year, there were lots of reader competitors as well as things like Apple's iPad. Elasticity of demand increased at that point and manufacturers responded by dropping prices to keep sales up.