1. Mass, Weight and Gravity

2. Student Learning Objectives
Students will be able to explain mass of objects with reference to a basic atomic structure
Students will be able to differentiate between mass and weight
Students will be able to calculate weight using the formula
Force = mass x acceleration due to gravity
Students will

3. WHAT IS GRAVITY ? A force of attraction between any two masses
It is not only an attraction between an object and the earth
It is an attraction between all masses in the universe

4. MASS The amount of matter or “stuff” an object contains
This matter or “stuff” is atoms, the small particles everything in the universe is made of
Atoms contain:
Nucleus – Protons and Neutrons
Electrons

5. MASS What is the unit of measurement of mass?
The more matter an object contains the greater its mass
An object’s mass stays the same wherever it is
G or kg

6. WEIGHT The force on the object is due to gravity Weight is a force
Force = Mass x Acceleration due to gravity
Weight changes based on acceleration due to gravity
The unit of weight is Newton (N), named after the scientist Isaac Newton
weight" is a measure of the gravitational pull between two objects.
A spring scale (e.g., the typical bathroom scale), balance scale compares masses; it will read the same on the moon.

7. Gravity (Mass)
The size of the force depends on the mass of the objects. The bigger the object, the bigger the gravitational force!
Small attractive force
Bigger attractive force

8. Gravity (Distance)
The size of the force also depends on the distance between the objects. The closer the objects the greater the gravitational force.

9. Free Fall
Objects whose only acceleration is due to gravity are in free fall.
Theoretically, objects in free fall continue to accelerate as long as they are falling.
All free falling objects accelerate at the same rate regardless of their mass. (9.8 m/s2)

10. Air Resistance
Air resistance is an upward force exerted on an object as it falls by air
It is, in essence, a frictional force
For simplicity, the amount of air resistance is determined by two factors
The cross-sectional area of the object
The speed of the object

11. Unbalanced Forces Air resistance is pushing upwards
Gravity is pulling to the ground

12. Help the kids with their discussion.
Which will get to the ground first in free fall, the elephant or the feather?
Does air resistance have anything to do with it?
Obviously, it’s the ……
Free fall: A situation where the only force acting on the body is due to it’s weight.
What is free fall?

13. What happens if you drop an elephant and a feather at the same time
What happens if you drop an elephant and a feather at the same time? Which will hit the ground first?
Why?
The force of air resistance is greater on the elephant because of its size and shape.

14. What if gravity was the only force acting on the elephant and the feather?
They would both fall at the same speed due to the earth’s gravity. This is known as freefall.

15. Conclusion
A greater acceleration due to gravity cause a greater weight.
A smaller acceleration due to gravity cause a smaller weight.
???
294

16. Conclusion
If all objects have the same acceleration on earth, once there is no resistance from air they will fall at the same rate.
9.8 m/s
I want students to know objects fall because of gravity. Gravity causes an acceleration on all objects that can be calculated like we did in the experiment. We need free fall to calculate the correct acceleration due to gravity.