$5. In this activity you have considered mostly cases in which you compared the motion of two objects for which only the force strength or the mass was different. But what if you had two objects that both had different masses and were both acted on by forces of different strengths? How could you predict which object's speed would change at a faster rate under these circumstances? Two students were discussing their ideas about a relationship that they could use to help them decide: FM-52MacBook Pro Unit FM $6. Some students have a race between two different fan carts. Cart A has a mass of 0.5 kg and a fan strength of 0.3 N. Cart B has a mass of 0.7 kg and a fan strength of 0.4 N. Which cart will win the race, and why??them, indicating that something about them was the same? (In effect you are trying to develop an equation involving force strength and mass that gives the same final result for each cart.) Summarizing Questions First discuss these questions with your group and note your ideas. Leave space to add any different ideas that may emerge when the whole class discusses their thinking. S1. When a single force acts on an object, how does the rate at which its speed changes depend on the strength of that force? Is this true for both increasing and decreasing speed? What evidence supports your answer? FM-50Activity 5: Changing Force Strength and Mass $2. To the right is a speed-time Speed versus Time graph for a cart that was given a 100 quick push along the track and 80 then gradually slowed down. 60 Which force do you think was Speed (cm/s) 40 stronger - the initial push or the one that slowed it down? How 20! do you know? 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Time (s) S3. How does the mass of an object affect the rate at which its speed changes while a force acts on it? What evidence supports your answer? S4. At a practice session, a soccer goalie is practicing rolling a soccer ball along the ground. To improve his strength, he also practices rolling a bowling ball. The coach measures the speed of both balls and sees that, manwhen the goalie pushes as hard as he can, the soccer ball has a speed of 15 m/s just after it leaves the goalies' hands, but the bowling ball has a speed of only 2 m/s. Write an explanation for why the bowling ball's speed is much less than the soccer ball's speed just after they left the goalie's hands. Assume the goalie applied the same strength force to both balls for the same amount of time, FM-51Activity 5: Changing Force Strength and Mass We saw that the greater the force strength, the I agree with what you say about the faster the speed changes. I also think that the force strength, but the speed of the more mass an object has, the faster it slows down, cart with more mass increased at a so increases in the force strength and mass both slower rate, not a faster one. I think produce a faster change in speed. That makes me you have to divide the force strength think the rate at which the speed of an object by the mass to find out about the rate changes depends on the force strength multiplied at which the speed will change. by the mass Amara Han In terms of a mathematical relationship, Amara thinks: Rate of change in speed = Strength of force x Mass of object, while Han thinks: Rate of change in speed = Strength of force Mass of object Do you agree with Amara, Han, or neither of them? What evidence from this activity supports your thinking