Lessons 7 and 9 Notes

“Rolling Along” and “The Fan Car”

1. The force of the roll is the unbalanced force that gets the ball rolling.

2. Inertia allows the ball to keep rolling.

3. There is friction acting between the ball and the ground allowing it to roll instead of slide.

• Newton’s Second Law of Motion: Acceleration is produced when a force acts on a mass.

• The fan is the force that causes the fan car to move forward.

Lesson 7: “Rolling Along”• In this inquiry, we rolled a steel ball across the

classroom and we measured the average speed.

Distance TraveledAverage Speed = _______________________

Time

 The units for average speed for these inquiries are meters/seconds or m/s.

Forces Acting on the Steel Ball:• The unbalanced force acting on the steel ball

to move it forward was the force of the roll.– Friction was the force between the ball and the

ground.– Gravity was the force that kept the ball on the

ground.

Newton’s First Law of Motion: An object in motion stays in motion unless acted on by an unbalanced force. An object at rest stays at rest unless acted on by an unbalanced force.• Newton’s First Law of Motion is also known

as the “Law of Inertia”.• Inertia is what keeps the steel ball in motion

after it has been rolled.

Examples of Newton’s First Law of Motion:• The Steel Ball (Lesson 7) – The steel ball will

stay in motion until it hits a wall (unbalanced force).

• The Fan Car (Lesson 9) – The fan car will not move until the fan (unbalanced force) is turned on.

Kinetic Energy is energy associated with moving objects. The steel ball and the fan car have kinetic energy.

Kinetic Energy = 1/2mv2

 Kinetic Energy = (1/2 x mass) x (velocity)2

 

Kinetic Energy is measured in Joules (J).

An increase in mass or speed will cause an increase in kinetic energy.

Example Problem:

If the mass is 4 kg and the velocity (speed) is 1.8 m/s. What is the kinetic energy?

 

Step 1: Multiply the mass by ½.

 

Step 1: ½ x 4 kg = 2 kg

 

Step 2: Square the speed.

 

Step 2: (1.8)2 = 1.8 x 1.8 = 3.24 m/s

 

Step 3: Multiply the two answers together.

 

Step 3: 2 kg x 3.24 m/s =

 

Step 4: Record your answer in Joules (J).

 

Step 4: 6.48 J

Lesson 9: “The Fan Car”• In this inquiry, we used the fan car with the fan off and with the fan

on to see the change in motion/speed.

 • Fan Off: The unbalanced force moving the car forward is the

student pushing it. The motion of the car was quick immediately after the push but then slowed down and eventually stopped because friction was acting on the car.

 – Hard Push – the car went faster for a longer distance.– Soft Push – the car went slower and did not go as far.

 • Fan On: The unbalanced force moving the car forward is the fan.

The motion of the car increased in speed over time. The car did not stop until it hit something or until the fan ran out of energy (batteries).

Forces Acting on the Fan Car:• Friction is working between the car’s wheels

and the floor.• Gravity is keeping the car on the ground.• Air resistance is going in the opposite

direction to the motion of the car.

Newton’s Second Law of Motion: Acceleration is produced when a force acts on a mass.

Example of Newton’s First Law of Motion: • When the fan (force) was turned on, the car

(mass) moved forward (accelerated).• Basically the force of the fan caused the car to

move out of rest and into motion, which is a change in speed (acceleration).