Lesson 10/5

Lesson 10/5

Open Ended

Journal - Chop Wood Carry Water

How much do you weight?

• In person come up and record your weight

• Virtual go jump on a bathroom scale if available and record your weight.

• What is this value telling you?

What is weight?

Now that you know how much you weigh, we need to figure out what exactly that number is telling you?

What is weight?

When you step on the scale, the only force acting upon you is the gravitational force due to the Earth's mass. So, what exactly what is weight? It is the gravitational force experienced by an object.

What is weight?

Remember that gravitational force is a field force whose magnitude is directly proportional to the mass of the object experiencing the force? In equation form, the gravitional force, which equals weight, can be written as F_g=mg. The mass of the object is m and g, called the gravitational field, is a vector quantity that relates the mass of an object to the gravitational force it experiences at a given location.

What is weight?

Near Earth's surface, g is 9.8 N/kg toward Earth's center. In other words, objects near Earth's surface experience 9.8 N of force for every kilogram of mass.

Scales

When you stand on a scale, the scale exerts a force upward on you. Because you are not accelerating, the net force acting on you must be zero. Therefore, the magnitude of force exerted by the scale (F_{scale on you}) pushing up must equal the magnitude of F_g pulling down on you. Inside the scale, springs provide the upward force necessary to make the net force equal to zero.

Scales

The scale is calibrated to convert the stretch of the springs to a weight. The measurement on the scale is affected by the gravitational field on Earth's surface.

Poll

Where would your weight be greater?

• Earth

• Mars

• Jupiter

Practice Problems

Google Classroom or on Paper

Open Ended

Exit Ticket - How can Newton's 2nd Law of Motion be used to determine weight?