Natural Science Summarizing Questions
S1:Return to the description of short car trip in the Initial Ideas section at the beginning of this activity. Below, sketch what you think a speed-time graph of the compete trip would look like, and label the different segments of your graph according to what the motion of the car is like during that period. Also, draw your graph on one half of a large presentation board.
Imagine taking a short trip in your car. When you first start out, you push on the gas pedal, the car starts moving and then picks up speed as you pull away. Once you reach a reasonable speed you set your cruise control and your speed then remains constant for a while. However, as you approach your destination you use the brakes to slow the car down and make it stop.
S3:Write a few sentences to describe the motion of the object represented on the speed-time graph shown below. In your description you should also explain briefly how you determined the motion from the graph.
S2:Another example of an applied mechanical interaction is when a soccer player kicks a soccer ball. Complete the energy diagram below for this interaction.
S2:What two types of energy change took place for the objects involved in the Elastic Mechanical Interactions you examined?
S3:What type of energy transfer takes place during an Elastic Mechanical Interaction? What evidence supports this idea? (You may want to look back to Activity 2 to answer this question.)
S4:Complete the following energy diagrams for two of the Elastic Mechanical Interactions you studied in this activity.
Launching a cart with a rubber band
A cart slowing down as it runs into a rubber band
S2:What are some similarities and differences between a Friction Mechanical Interaction and other types of Mechanical Interaction?
S3:What type of energy decreases when a moving object is slowed during a Friction Mechanical Interaction? What type of energy increases? In which object(s) does this energy increase occur?
S4:Complete the energy diagram below for the cart slowing down gradually as it moves.
S6:Suppose it were possible for you to start an object moving, and then arrange for it to be free of the influence of any mechanical interactions. What do you think its motion would be like? Explain your reasoning.
S1:When the hand is exerting a force on the cart, what is the motion of the cart like? What evidence from this activity supports your idea?
S2:Do you think the force of the hand was transferred from the hand to the cart during the interaction and then continued to act on it after contact was lost? What evidence supports your idea?
S3:At what moment do you think the force of the hand stopped acting on the cart?
S4:During a mechanical interaction what do you think is transferred from the source to the receiver; energy, force, both, or neither? Explain your reasoning.
S1:If a cart is at rest and an unbalanced force acts on it, what happens?
S2:If the same unbalanced force continues to act on the cart what happens to its motion?
S3:In general, during the time an unbalanced force with a constant strength acts on a moving object, in the same direction as its motion, what is its motion like? Does it move at a constant speed, does its speed continuously increase, or does its speed continuously decrease? What evidence supports your thinking.
S4:If the unbalanced force suddenly stopped acting while the object was moving (for example, if a wire on the fan broke) what do you think would happen to the motion of the object? Explain your reasoning.
S5:When you were using your finger to try to push the cart with a constant strength force, you probably noticed the cart was ‘getting away’ from you. (If not, try it again.) Why do you think the cart behaved in this way?
S6:You have probably noticed by now that all the ‘Developing Ideas’ activities in the PET course have a similar (though not identical) structure. This structure is intended to help you in the development of your own ideas.
S1:If an object is already moving, what effect on its speed does an unbalanced force applied in the opposite direction to its motion have?
S2:If such an unbalanced force continues to act what else may happen?
S3:Shown below are two force diagrams for a cart upon which an unbalanced force (from a fan unit) is acting. What will the motion of the cart be like in each case? Explain your reasoning.
S1:Why do you think most moving objects we see around us eventually slow and stop?
S2:What evidence from this activity suggests that friction is a force that opposes motion?
S3:How is friction similar, or different, from other forces you have used to slow objects down?
S4:Why do you think the block slows down more rapidly on the sandpaper than on the bare table-top?
S5:Even when sliding across the apparently smooth table-top the block still slows down and stops. Why do you think this is?
S1:How does the motion of an object acted on by an unbalanced force depend on the strength of that force? What evidence supports your answer?
S2:In practical terms what does your idea imply about the strength of the force acting on object when it is speeding up quickly (such as an aircraft on take-off) or slowing down only gradually (such as when it approaches the gate after landing).
S3:How does the mass of an object affect how quickly, or how slowly, an unbalanced force can change its motion? What evidence supports your answer?
S4:Which would it be easier to start moving, a beach ball or a bowling ball? Which would be easier to stop once it is moving? Why do you think this is?
S1:Earlier in Cycle 2 you saw that the effect of an unbalanced force is to change the motion of an object in some way (either speeding-up or slowing-down).
In Experiment #1 of this activity you saw a situation where two fan-units pushed on the cart in the same direction. Was the effect of this combination of forces similar to that of a single unbalanced force (perhaps of a different strength), or did it cause something different to happen? What evidence supports your answer?
S2:In Experiment #2 of this activity you saw a situation where two forces acted on the cart in opposite directions (the fan-unit and friction). When this combination of forces acted on the cart, was the effect similar to that of a single unbalanced force (perhaps of a different strength), or did it cause something different to happen? What evidence supports your answer?
S3:Shown below are two force diagrams for a moving cart. What would the motion of each cart be like in each case? Explain your reasoning.
S4:In Cycle 1 you were asked to think about the nature of the three types of questions in the activities: Prediction, Observation, and Inference.
Now that you have worked through more activities, look back through them and describe what you think the role of each question type is in helping you develop your own science ideas.
S1:When the forces acting on an object are balanced what happens to its speed? Does its speed change or does it remain constant? What evidence supports your idea?
S2:How does your answer to the previous question apply to an object at rest, with balanced forces acting on it?
S3: Two students were discussing their ideas about balanced forces:
DaveLuisa
How would you respond to Dave’s concern? (Hint: what is the motion of an object like if the force in one direction is stronger than the force in the opposite direction?
How would you respond to Luisa’s concern? (Hint: why did you have to give the carts an initial push to get them started when the forces were balanced? Were the forces balanced during the push?)
S4:Use the pictures below to draw three force diagrams for the cart with balanced fans acting on it; one before the initial push, one during the initial push, and one after the push. Explain your diagrams below the pictures.
Before the push /
During the push /
After the push
S1:Do magnets have to touch each other to interact? How do you know?
S2:You probably found it difficult to identify the energy source in some of the magnetic interactions. Why was this?
Does the strength of the influence on the compass depend on how far it is from the bar magnet? How do you know?
Does the influence on the compass change, depending on which end of the bar magnet it is closest to? Explain how you know.
S1:How could you account for the two aspects of electric charge interactions you have observed in this activity:
- Charged objects can interact with each other without touching.
- In some electric charge interactions both objects start moving as a result of the interaction.
S2:Complete the energy diagram below for the electric charge interaction between two hanging wool-rubbed knives.
S1:While an object is falling toward the ground is it an energy source, or an energy receiver (or neither)? Explain your reasoning.
S2:How can you account for the observation that objects close to the Earth feel its influence, even when they are not touching it? (Hint: How have you accounted for this behavior in other interactions.)
S3:In the gravitational interaction between the Earth and a falling object you only see one of the objects involved move (the one that falls). Do you think the Earth moves too? If so, why don’t you observe its motion?
S4:Complete the energy diagram below for the interaction that caused the ball to fall, when you released it.
S1:Does the strength of the gravitational force of the Earth pulling an object toward the ground depend on the object’s mass? What evidence supports your answer?
S2:What other force, apart from the gravitational force of the Earth, acts on falling objects? What types of object are affected most by this force?
S3:If the force of air resistance is negligible, does the rate at which an object falls depend on its mass? Why do you think this is?
S4:Does the strength of the force due to air resistance seem to depend on how fast an object is moving? If so, what would happen to the strength of the force of air resistance acting on an object as it falls? How would this eventually affect its motion if it fell for long enough?