1. Motion and Forces

2. Types of Forces Gravitational Electromagnetic Frictional
Strong and Weak Nuclear

3. Gravitational Forces
Force of attraction between all objects as a result of their masses and distances between them.
The higher the masses and the shorter the distances between two objects, the greater the force of gravity.
The smaller the masses and the larger the distances between two objects, the weaker the force of gravity.

4. Gravity exists between ANY two objects

5. Why things fall to the ground
When we drop an object, the force of gravity is strong because the earth has a large mass and is close by. The object gets pulled to the ground.
Near the Earth’s surface, objects accelerate to the ground at a rate of 9.8 m/s2, regardless of their masses.

6. The gravitational force of the Earth decreases as you move away from the planet.
Different planets and stars will have different forces of gravity at their surfaces due to their different masses. The bigger the object the greater the force of gravity.
Gravitational forces also explain the Earth’s tides

7. Mass vs. Weight
Mass is a measure of the quantity of matter in an object. This does not depend on where the object is.
Weight is a measure of the gravitational force acting on an object. This DOES depend on where the object is.

8. Weight However, weight and mass are different, how come?
weight = Fg = mg which is similar to F=ma
m - is mass measured in kilograms (kg)
g - gravitational field intensity measured in Newtons/kilogram (N/kg); this is also known as acceleration (m/s2).
Fg - is the force of gravity measured in Newtons (N)

9. 1 N = 1 kg x m s2
We know that earths gravitational pull is 9.8 N => kg x m = m kg s2 x kg s2

10. Example
What is the gravitational force (weight) of a 60 kg astronaut on the earth’s surface? Intensity of gravitation on earth is 9.8 N/kg
F = mg
F = 60 kg X 9.8 N/kg
F = 588 N

11. Example
What is the gravitational force (weight) of a 60 kg astronaut on the Moon’s surface?
F=mg
F= 60 kg X 1.67 N/kg (force of gravity on the Moon)
F= N

12. Gravitational Intensity on the Planets in our Solar System
Acceleration (m/s)
Intensity (N/kg)
Mercury
3.7 m/s²
3.7 N/kg
Venus
8.87 m/s2
8.87  N/kg
Earth
9.8 m/s2
9.8  N/kg
Moon
1.62 m/s2
1.62  N/kg
Mars
3.71 m/s2
3.71  N/kg
Jupiter
24.79 m/s2
24.79  N/kg
Saturn
10.44 m/s2
10.44  N/kg
Uranus
8.69 m/s2
8.69  N/kg
Neptune
11.15 m/s2
11.15  N/kg
Pluto
.658 m/s2
.658  N/kg

13. How much do you really weigh???
Take your weight in kg (pounds/2.2) and calculate how much weight in Newton’s you are on all the planets in our solar system.

14. Electromagnetic Force
Force of attraction or repulsion between two charged objects or between the poles of two magnets
We already discussed this earlier in the year
Likes repel, opposites attract

15. Frictional Force
The force that prevents two objects from slipping over each other
Air resistance is also a force of friction
Friction depends on:
The smoothness of the surfaces (the rougher the surfaces the greater the friction)
The pressure between the surfaces (the greater the pressure the greater the friction)

16. Friction

17. Strong and Weak Nuclear Forces
Act within the nucleus of an atom
Short range forces
Holds the nucleus together

18. Hippo & Ping Pong Ball In a vacuum, all bodies fall at the same rate.
If a hippo and a ping pong ball were dropped from a helicopter in a vacuum (assuming the copter could fly without air), they’d land at the same time.
When there’s no air resistance, size and shape don’t matter!

19. Video of a Vacuum and two objects
Question why do both objects fall at the same acceleration?

20. Table of Equations from this unit
Kinetic Energy
KE = ½mv2
Speed of an Object
d=vt
Acceleration
a = change velocity change of time a=∆v ∆t
Force
F=ma
Weight
Fg = mg

21. Measurement
Definition
Unit
Symbol
Kinetic Energy
Amount of energy needed to move an object
Joules J
Mass
How heavy an object is in kilograms
Kilograms kg
Velocity
How fast an object is moving in meters/second
meters/second
m/s
Distance
The distance from one point to another point
meters m
Time
Amount of time measured in seconds
seconds s
Acceleration
The rate of change of velocity per second
meters/second2
m/s2
Force
The amount of effort required to move an object
Newton N
Force of Gravity
The amount of gravitation pull on an object.
Gravitational Pull
The intensity of gravity measured in N/kg
Newton/kilogram
N/kg