# Investigation 1 – PostLab ### ANALYZE IT

Analyze the activity in which you pulled the woodblock 1m.

• What is the resistance to motion that you feel as you pull the block?
• What force keeps the block from slowing down?

As a class, discuss acceleration:

• Between the two lines, did the block slow down, speed up, or change direction?
• Acceleration is a change in velocity. What was the acceleration of the block pulled between the two lines?
• Can an object have an acceleration of 0 m/s2 while the object is moving?

Perform the following calculations.

• The block you pulled had an acceleration of 0 m/s2. Use the formula ΣF = ma to determine F. Remember than ΣF represents the sum of the forces, not just the force exerted to pull or just the force of friction on the block.
• Using this formula, calculate the frictional force between the block and the table.

Note: You may be confused by the “negative” force. Remember that the negative number indicates the direction of the force of friction. The applied force was a positive number. Since force takes into account magnitude and direction, the frictional force was a force of the same magnitude in the opposite direction of the applied force.

Discuss the energy transfer which occurred between the woodblock and the table.

• What type of energy was present as the woodblock was moved across the table?
• As the block slowed, what happened to the kinetic energy?
• The Law of Conservation of Matter and Energy states that energy and matter are never produced nor destroyed. According to this principle, what happened to the kinetic energy of the block?

Note: If you have a difficult time understanding this transformation from kinetic to heat energy, rub your hands together vigorously.

• What form of energy do your hands have?
• While rubbing your hands, how do they begin to feel?
• Into what type of energy was kinetic energy transformed?
• What factors do you think influence the frictional force?

Be able to generate hypothetical experiments to test your ideas about influencing factors of frictional force between two surfaces.

Record these experiments in your Investigation 1 Student Data Record.

### GET FOCUSED

Complete the Focus Questions in your SDR then discuss them as a class.

• What is the relationship between speed, velocity, and acceleration?
• How does the frictional force affect motion?