# Unit F: Energy Sources and Motion

## How fast can a human run?

### 1. Get Set to Explore

#### Vocabulary

• miles per hour: A measure of speed; the number tells how many miles an object, animal, or person can travel in one hour.

#### Building Background

• Ask children which they think can go faster, a person or a car. Children can give their answers with a show of hands. Then ask them how they would measure the speed of these two. Elicit the idea that we often measure the speed of a car in miles per hour. Go over the definition of this term. Then ask children to define it in their own words, to make sure that they understand it.
• Tell children that in this simulation, they will watch races between a cheetah, a horse, a rabbit, a turtle, and a human. Ask children to predict which of the five is the fastest and which is the slowest. Ask them to write down their predictions and the reason they think the winner will win and the loser will lose. Encourage children to relate their reasons to specific traits, such as weight, leg length, body shape, etc.
• Present the Discover! question: How fast can a human run? Elicit predictions from the class and write them on the board. Ask children to give you their answers in miles per hour. Have volunteers explain why they picked the speed they predicted. Select three predicted speeds: one high, one low, and one in the middle. Ask the class to vote on which one they think is the maximum speed a human can run. Tally the votes on the board.

### 2. Guide the Exploration

• Have children launch the Discover! Simulation, listening closely to the question and the directions.
• Explain that children can enter up to three racers in each race. To enter a racer, they need to click the racer and it will appear at the starting line. When all the racers are in place, they should click Start, and the race will begin. Point out that the speedometer for each racer shows that racer's speed in miles per hour. Tell children that by moving the cursor over the speedometer at the end of a race, they can hear how fast each racer went. Encourage children to run races with all of the different racers. They should record the speeds each racer reaches.

### 3. Review/Assess

• Go over Step 3's Wrap-Up text with the class. Let the class compare the fastest speed human runners have been able to run with the predictions they made before doing the simulation. Explain that human racers can run about as fast as a car goes when the driver is going the speed limit through a school zone.
• Make sure that children understand that most people cannot run 23 miles per hour, even for a short time. An Olympic athlete sprinting in a fairly short race attained this speed. Many people cannot run half as fast as this athlete, even for a short distance.
• Present the Extension question to the class.
• The racers are rated in order from fastest to slowest as follows: cheetah (65 mph); horse (50 mph); rabbit (35 mph); human (23 mph); turtle (0.16 mph).
• The cheetah is the fastest racer.
• The turtle is the slowest racer.

If time permits, present children with the following questions:

• Critical Thinking Draw Conclusions Why do you think the turtle is so slow? Hint: Look at the turtle's size; look at its shape; look at the length of its legs. Answer: Guide students to recognize that the turtle's shell is very heavy; they should notice that it has a round, squat shape in comparison with the horse, the cheetah, and the rabbit, which all have a sleek shape; finally they should note that the turtle has relatively short legs compared to its body size. These three features help explain why the turtle is slow.
• Inquiry Skill Use Numbers How much faster is the cheetah than the horse? How much faster is the horse than the rabbit? How much faster is the rabbit than the human? Tell how you figured out each answer. Answer: The cheetah is 15 mph faster than the horse; the horse is 15 mph faster than the rabbit; the rabbit is 12 mph faster than the human. To find each answer children need to subtract the speed of the slower animal from that of the faster animal.

### 4. Reaching All Learners

#### Challenge

Challenge children who are interested in animals to find out about other fast animals. They should research which bird is the fastest flyer, which ocean-dwelling animal is the fastest swimmer, and what other animals run very fast on land. Encourage children to use the Internet to search for answers. Give them time to share the information they find with the class.