Activity 78 Analysis1. Look at your graphed line for “Experiment

1.” Explain why it does or does not indicate that there is a relationship between force and acceleration.

It does indicate a relationship because in both experiments, as the force increases, so does acceleration. In this case the graph shows that the relationship between force and acceleration is linear because the best fit for the data set is a straight line.

2. Compare the two lines, “Experiment 1” and “Experiment 2” on your graph. Identify and explain:

a. any similarities.

The similarities are that both plots show a direct relationship between force and acceleration, both have straight lines that go through the origin, and both have a positive slope. This is a result of graphing the relationship F = ma when the mass is held constant. In this situation, force versus acceleration will always be a straight-line graph that goes through the origin and have a slope equal to the mass.

b. any differences

The major differences in the graphs is that the second plot has a steeper slope. The slope on “Experiment 2” is steeper than the slope from “Experiment 1” because the mass is 4 kg in “Experiment 2” and the mass is 2 kg in “Experiment 1”.

3. Use your equation for force, mass, and acceleration to find the missing values in the table below.

Experiment 3

Force (N) Mass of Block (kg)

Acceleration of Block (m/s2)

25 5 5

20 2 10

10 5 2

50 10 5

100 4 25

1,000 40 25

4. In the first activity, Vehicle 2 has greater acceleration than Vehicle 1, but has a less forceful engine. How can this be? Explain in terms of your equation.Vehicle 2 can have a greater acceleration with less force if it has a lower mass than Vehicle 1. Newton’s equation F = ma, can be rewritten as a = F/m, which shows that acceleration is the ratio of force to mass. Thus, for an object to obtain a higher acceleration with less force, it must have less mass.

5. One newton of force is the same as 1 kg x 1 m/s2. Use your equation to explain why this makes sense.

Since force, measured in newtons, is equal to mass times acceleration, the unit of force, must be equal to the unit of mass (kg) times the unit of acceleration (m/s2), which is known as the compound unit of kg- m/s2.

Activity 78 Major Concepts

• There is a direct relationship between the force applied to an object and its resulting acceleration.

• When an object is subject to a force, there is an inverse relationship between its mass and its resulting acceleration. In other words, with the same applied force, an object with a smaller mass will have greater acceleration.

Activity 79

Title: Inertia Around a Curve

Read E-25

Problem: How does inertia affect how an object moves?

Hypothesis: If _______________, then ____________________.

Moving and Changes in Motion• Moving is any change in position.

• What is a change in motion?

• A moving object does not necessarily have a change in motion. An object traveling in a straight line at a constant speed is moving (changing position), but in not changing its motion (not accelerating) because neither its speed nor its direction is changing.

Inertia• Which type of car, a heavier or lighter

one, needs more force to slow down with the same deceleration?

A car with more mass needs more force to slow it down.

Copy this into your notebook!

Background information:

Inertia IS NOT a force. It is a word that describes the tendency of an object to keep moving on its current path and at its current speed.

Qualitative vs. Quantitative

• Today is a qualitative day.

• We will be making observations that do not include recording numbers or measuring distances or times.

• Take your time with your observations.

Demonstration

 http://www.youtube.com/watch?

v=6gzCeXDhUAA&feature=related

Review Procedure

Possible Pitfalls

• Irregularities on the table and any spin on the marble may cause the marbles to veer from its intended path.

• The path of the lower mass glass marble is more likely to be affected by forces applied to it after it leaves the track.

• If you are having trouble getting consistent results, send the marble around the track at a higher speed.

• Make a barrier around your table with books and rulers

• Don’t tell me you lost your marble. Find it. It is somewhere. Mass is neither created nor destroyed.

Follow-up• Read and compare analysis questions 1

and 2

• The term inertia describes the tendency (and not the force) of an object to keep going in a straight line at a constant speed even when there are no forces acting on it.

• How do the sides of the circular track wall affect the motion of the marble?

• What happens when the marble exits the track?

After Data/Evidence, compile a list of all changes in motion of the marble and name the forces that were responsible.

List of Forces Responsible for Change of Movement

Change in Motion Force Responsible

Homework• Answer Analysis questions 1-3

• Be ready to trade and grade PH assignment from Tues/Wed on Monday

• Update Vocabulary