Explain why the human heart rate increases when exercising.

Sally and sue were investigating the topic of friction in science. they used a small car and a ramp as seen in the picture to test what they were learning. they knew that they slipped easily on waxed floors but not on carpet, so they decided to change the material on the surface of the ramp to see what happened. they planned to use glass, carpet, aluminum foil, and sandpaper and run the car down the ramp over each surface. what would be the best research question to guide the girls' experiment? a) does the amount of surface area affect the friction on the moving car? b) will the car travel fastest on the glass surface? c) how does the angle of the ramp affect the speed of the car? d)do rougher surfaces tend to create more friction than smooth surfaces?

The term autotroph refers to an organism that: a. uses co2 for its carbon source. b. must obtain organic compounds for its carbon needs. c. gets energy from sunlight. d. gets energy by oxidizing chemical compounds. e. does not need a carbon source

Currents are caused by temperature and density differences