1. a snowball rolling down a hill accumulates snow and becomes larger, which increases its speed, causing it to increase its size and speed even more. positive / negative.
2. increasing air temperatures from global warming speed up the melting of glaciers, exposing darker rocks underneath the ice. the dark surfaces absorb more sunlight, causing further increases in temperature and accelerated glacier melting. positive / negative.
3. a dog pants as it lies in the hot summer sun, releasing excess body heat to the environment and lowering its body temperature to its stable state. positive / negative.
4. a bull on the edge of a herd of cattle panics when it hears a loud noise and begins to run. five nearby cattle sense the panic and also begin to run. this causes another 15 cattle to panic. eventually, all 100 cattle in the herd panic and stampede. positive / negative.
5. you invest $1,000 in a savings account and reinvest the 5% interest you earn. the interest makes the amount of money in the account larger, so it earns even more interest. after 20 years, the account contains more than $2,600 and is still growing. positive / negative.
6. when blood sugar levels rise after eating a meal, the pancreas releases the hormone insulin, stimulating cells to take up sugar from the blood. when blood sugar levels drop, the pancreas releases another hormone to stop sugar uptake by cells. positive / negative.