Question 1: A large fan, turned on high, is blowing air across a flat and level table. If you roll a tennis ball across the table, will it go straight? Why or why not?

Student response: No, it will curve due to the force of the fan blowing on the ball.  It will go straight unless a force causes it to change directions.

Question 2: In the situation above, what path will the ball take if the fan is turned off?

Student response: The ball will go straight.

Question 1: If you had two plates, one with a 1/8 wedge cut out of it and one with a 1/4 wedge cut out of it, would the path of a marble rolled around the edge of the plate be different when it leaves the plate with the smaller wedge than when it leaves the plate with the larger wedge? Explain your answer.

Student response: Regardless of the size of the opening, so long as the marble doesn’t hit the opposite edge of the cutout, the ball will begin to move in a straight line once the curved edge of the plate is not in place to force the marble in a circle.

Question 2: Keep thinking about the activity with the plate and the way the marble behaved. Why are there guardrails on the edges of highway curves?

Student response: Guardrails are designed to keep cars on the road should they move too far to the side. In other words, the guardrail is designed to force cars around the curve and to help cars avoid the ditch. This question is similar to the marble activity where the edge of the plate keeps the marble moving in a circle.

Question 3: Let’s go back to the last activity we did with the swinging object. Think of other objects that move around, or orbit, larger objects. Is there a string the keeps planets in orbit around the sun or a string that keeps the moon in orbit around the earth? What is the invisible string that keeps the moon from flying away?

Student response: gravity! Without gravity, the planets would fly away from the sun, and the moon would fly away from the earth.

Question 1: inertia is defined as the tendency for an object to resist change in motion. In other words, an object at rest stays at rest, and an object moving in a straight line continues in a straight line unless acted on by a force. You are riding in a car traveling at 70 mph. The car suddenly decelerates to zero. What does the inertia of your body want to do? What safety precautions are in place to make sure that doesn’t happen?

Student response: Your body is independent of the vehicle. Even if the vehicle stops suddenly, your body wants to keep moving. Your body has mass, therefore
it has inertia. It wants to keep moving in the straight line with your car. Once the car stops, unless you are wearing something to keep you in the car, you will most surely fly through the windshield and end up lying on the side of the road wondering why you didn’t buckle the seatbelt! Seatbelts are safety devices designed to keep you in the car.

Question 1: Think about a football game. What does mass have to do with what position you play? Why do the biggest football players usually play the line positions?

Student response: They need to protect the other players. It takes more force to move them because they have more mass.

Question 2: If you were hit with a ping-pong ball and a golf ball thrown with the same force, which would hurt more? Explain your answer.

Student response: Getting hit with the golf ball would hurt more because it has more mass.

Question 3: Most people can throw a baseball further than a 12-pound shot put. Why?

Student response: The baseball has less mass so it takes less force to throw it than it takes to throw the heavy shot put.

Question 1: Racing bikes are made to be very light. What would be the advantage to having a lighter bike?

Student response: Because of the smaller mass of the bike, it takes less force to make it go. The rider could make the bike go faster without using as much force.

Question 2: Some bowlers like to use a very heavy ball. What advantage could this give to a bowler?

Student response: Even if you could roll both bowling balls at the same speed, the ball with more mass would have more force when it hit the pins. A heavy ball would exert more force on the pins compared to a lighter ball rolled at the same speed.

Question 3: Could a person use a lighter bowling ball to exert the same force on the pins? Explain your answer.

Student response: Yes, if the person rolled the lighter ball faster (with more force) than the heavy ball.

Question 1: How would the acceleration of a chain of five shopping carts compare with the acceleration of a single cart if the same force acted on both?

Student response: Using the same force, the acceleration would be less on the chain of carts than on the single cart because the chain of carts has more mass than a single cart. Using the same force, the object with less mass will accelerate more.

Question 1: Brent and Bryan are sitting in rolling chairs facing each other. They are both holding a bathroom scale in their hands with the dials facing them. If Brent pushes Bryan with a force of 20 pounds, how much force will Bryan exert back toward Brent?

Student response: 20 pounds

Question 2: What will be the reading on the scales if Brent’s chair is backed up against a wall and they push against each other?

Student response: Both scales will read the same.

Question 3: Bryan and Brent weigh the same. If Brent pushes Bryan, who will roll further?

Student response: Both will roll the same distance.

Question 1:  Mark weighs twice as much as Brent. If Mark pushes Brent with a force of 25 lbs, how much force will Brent exert back?

Student response: 25 lbs of force

Question 2: Mr. Smith weighs five times as much as Brent. If he pushes Brent with a force of 100 lbs, how much force will Brent exert back?

Student response: 100 lbs of force

Question 3: If Jenny is lying on her back and pushes a book up with a force of 5 lbs, how much force is the book exerting back?

Student response: 5 lbs of force

Question 1: Let’s look at Newton’s Third Law and how it relates to sports. Any sport where you hit an object applies here, but let’s look at baseball specifically.  Imagine that you are a pretty good hitter, and your favorite pitch is a fastball right down the middle. You have a pretty good line of sight on the ball. You haven’t hit a homerun all year long, and this is the last game of the season.

Tommy is the starting pitcher and is getting tired. His fastball is only making it over the plate around 45 mph. It looks like a melon coming in over the plate, right down the middle. Jordan is in the bullpen warming up and is ready to replace Tommy. His fastball will be quite a bit faster. Remember, both pitchers throw the ball right down the middle, just at different speeds. You haven’t hit a home run all year.

Which pitcher gives you the best chance to hit one out of the park?

Student response: Regardless of the exact speed or force involved, the faster the ball is coming in, the faster it can leave the bat (equal and opposite reactions).  Jordan would have the higher speed fastball and would therefore have more force. If I swing the bat the same every time, I will have a better chance at hitting a home run off Jordan than off Tommy because Jordan’s pitch has more initial force so there would be a larger reaction force as well.

Teacher prompt: Students should be in groups of 3-4 for ease of taking measurements. Students may record their own data but will need help with the collection process. The students will construct a ramp at least one meter long (can be longer if space allows). Using books to prop up one end of the plank, students will release cars from the top of the ramp. They need to be sure to record the time it takes for each car to reach the bottom of the ramp from the time of release. They are also measuring the distance the car travels after leaving the ramp. The objective is to identify the relationship between mass, acceleration, and force as explained by Newton’s Second Law. They may also find Newton’s First Law helpful since it deals with the concept of inertia.

Extension:  For students who need a little something extra, allow them to change the height of the ramp or the distance up the ramp that the vehicle is released from. NOTE: It is crucial to emphasize the importance of only changing one variable at a time. If there are multiple variables being changed at one time, it becomes increasingly complicated to know which variable is responsible for the change in results.