Day 9 - Inertia and Momentum

(To download a pdf of this lesson click here. You will need Adobe Acrobat Reader. Get it here free.)

Teacher's Information:

Newton's Second Law of Motion states that an object is accelerated whenever a net external force acts on it. The net force equals the object's mass times its acceleration. F=ma

This law expresses the exact relationship between force and acceleration. For a given body, a larger force will cause a proportionally larger acceleration. Force and acceleration are both vectors. The direction of the acceleration of an object is the same as the direction of the net force acting on it.

Another way of stating Newton's second law is that an object's acceleration is equal to the net force acting on the object divided by its mass. This means that a large force acting on a large mass can result in the same acceleration as a small force acting on a small mass.

Newton's Third Law of Motion is a basic statement about the nature of forces in general. It is a simple law that adds and important perspective to the understanding of forces. It states that forces always come in pairs: when one object exerts a force on a second object, the second exerts an equal and opposite force on the first.

If you push against a wall with your hand, the wall exerts an equal force back on your hand. A book resting on a table exerts a downward force on the table equal to the weight of the book. The table exerts an upward force on the book also equal to the book's weight. The Earth pulls down on you with a force that is called your weight. Consequently, you exert an equal but upward force on the Earth.

Vocabulary:

Newton's Second Law: A force on an object will cause it to accelerate in the direction of the force. The greater the mass of an object, the harder it is to change its speed. This is the law of acceleration.

Newton's Third Law: For every action, there is an equal and opposite reaction. This is the law of interaction.

Materials needed:

• string (approximately 10 feet for each group)
• 50 long balloons
• 100 straws
• tape
• paper clips
• 25 small boxes (like a milk carton)
• paper board (to cut out circles for wheels)
• 25 pencils
• scissors
• paper

Introduction:

Tell students that today they will learn about Newton's second and third laws of motion. Remind them that his first law states that an object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an outside force.

Newton's second law states that a force on an object will cause it to accelerate in the direction of the force. Demonstrate this by asking for a volunteer. Have the student stand next to you and then give him or her a gentle push. Ask what happened? The student accelerated in the direction of the force (your push).

Go on to explain that Newton's third law states that for every action there is an equal and opposite reaction. When you pushed the student, you could feel a force against you. Our activities today will demonstrate these laws.