1. What Happens When Forces Act on Objects?
Lesson 1

2. Forces A force is a push or a pull A force has both size and direction
Some forces act only if the two objects touch; i.e. elephant on a ball
Other forces act even when the objects do not touch; i.e. Earth’s gravity on you or magnets repelling each other

3. Measuring Forces Force is measured with a spring scale
Spring stretches if the force is greater
Unit of measurement is a Newton
Newton is defined as the amount of force needed to change the speed of a 1 kilogram object one meter per second per second

4. Forces on an Object If forces are balanced, the object does not move
If the forces are unbalanced, the object changes speed and/or direction
Net force is the sum of all forces working on an object
5 N force to the right and a 3N force to the left, overall force is 2 N to the right

5. Friction
Friction is a force that resists the movement of one surface past another
Rough surfaces tend to create more friction than smooth surfaces
Rolling friction – resists the motion of a rolling object
Sliding friction – resists the motion of a sliding object
Static friction – resists the motion of an object just as it begins to move

6. Helpful and Harmful Friction
Helpful friction allows you to walk across the room without slipping
Friction on a brake to help you slow down
Harmful friction – Friction in a car engine can be harmful to metal engine parts if the rub against each other
Friction causes soil erosion and weathering
Wears away tires, soles of shoes

7. How does gravity affect objects?
Lesson 2

8. Gravitational Forces
Gravitational force is a force of attraction between any two objects
First explained by Newton in 17th century
Depends on two things – mass and proximity (how close)
Weight is the force of gravity pulling on you, less on the moon because the force of gravity is less

9. Gravity and the Universe
Gravity determine the motion of the planets and stars
The Sun is the most massive object in our universe, thus everything revolves around it
We don’t feel the gravitational pull of the Sun because we are not as close to it as we are to the Earth’s core

10. Tides A tide is the rise and fall in water level near the ocean shore
Moon’s gravitational pull has more of an affect on liquids than solids
The Moon’s gravity causes the tides in Earth’s oceans
We have two high tides each day because the water is being pulled away from the Earth; he other high tide is when the water gets pulled away on the opposite side