Relying on an animal to come by is risky. A flower may have to wait a long time for the right animals to come by. What if one never passes close enough to the flower? Hoping the wind will blow is also risky for a plant. What if the wind does not blow? What if the blowing pollen does not land on another flower? The wind could even blow the pollen over the ocean where it is wasted. Giving free nectar is costly. It is not a good use of the plants energy. A plant uses a lot of energy to produce nectar. Some animals may just drink the nectar. They may not carry off any pollen in return. To improve their chances, plants evolved special traits. For example, they developed ways to hide their nectar. Only certain animals were able to get at the plants hidden nectar. These specific animals might be more likely to visit only flowers of the same species. This was also a benefit for some animals. Animals also evolved special traits to get to the nectar.

Question: "Why is giving free nectar costly?"

Answer: "It is not a good use of the plants energy and it uses a lot of energy to make the nectar"

Response: yes

We drove about a great deal--the country at the back of Deauville, going away from the sea, is lovely--very like England--charming narrow roads with high banks and hedges on each side--big trees with spreading branches meeting overhead--stretches of green fields with cows grazing placidly and horses and colts gambolling about. It is a great grazing and breeding country. There are many haras (breeding stables) in the neighbourhood, and the big Norman posters are much in demand. I have friends who never take their horses to the country. They hire for the season a pair of strong Norman horses that go all day up and down hill at the same regular pace and who get over a vast amount of country. We stopped once or twice when we were a large party, two or three carriages, and had tea at one of the numerous farmhouses that were scattered about. Boiling water was a difficulty--milk, cider, good bread and butter, cheese we could always find--sometimes a galette, but a kettle and boiling water were entirely out of their habits. They used to boil the water in a large black pot, and take it out with a big spoon. However, it amused us, and the water really did boil.

Question: "What makes us think the speaker is a person of the upper class?"

Answer: "They have coins jingling in their pocket"

Response: no

What if two children push a swing at the same time? Would the swing go higher? Yes, together their force would be more. It is common for forces to be combined. Most objects on Earth have at least two forces acting on them. Do you know what one of them is? Of course, that force is gravity. How many forces do you have on you right now? Gravity pulls you down toward the center of Earth. Your legs exert a downward force. They hold you up against the pull of gravity. Consider the example in Figure 1.3. A book is resting on a table. Gravity pulls the book downward. It has a force of 20 newtons. At the same time, the table pushes the book upward. Its force is also 20 newtons. The table opposes the pull of gravity.

Question: "Give two examples of combined forces action on an object"

Answer: "Two children pushing a swing, book resting on a table"

Response: yes

So what is gravity? A typical definition of gravity is that it is a force. It causes an attraction between two masses. According to this definition, anything that has mass exerts a force. Any object exerts gravity on other objects. It does not matter how small it is, it has gravity. The more matter an object has, the more gravity it has. Your pencil has a tiny bit of gravity, but far too little to notice. What about a planet? It would have a lot of gravity. An objects gravity exerts a pull on other objects. Friction only occurs between objects that are touching. Gravity can act between objects that are not touching. In fact, gravity can act over very long distances. Where else can you feel gravity?

Question: "Does size matter when it comes to gravity?"

Answer: "yes"

Response:
no