1. Physics Unit 1
Force

2. Force – push or pull
A force always acts in a certain direction
ex. if you push something, the force is in the direction of the push
To describe a force you need to know direction and strength (size) of the force
ex. Push the box to the right with a force greater than 20 N

3. Net force Is the total force acting on an object To find net force:
Add forces acting in the same direction
Subtract forces acting in opposite directions

4. Forces in Nature Electric force Magnetic force Gravity ex. lightning
ex. magnetic poles
Gravity
ex. Falling objects – apple from tree

5. Weight Weight is a force
Weight is a measure of the amount of gravity acting on an object
To lift an object on Earth you must over come the gravity pulling on it, you must lift with a force equal to or greater than its weight

6. Newton
metric unit of force
named in honor of Sir Issac Newton

7. What is gravity? Sir Isaac Newton 1642 – 1727
The Law of Gravity or Universal Gravitation – states that all objects are attached to each other by the force of gravity

8. Gravity
force of attraction between all objects in the universe

9. Gravity
the larger an object’s mass, the greater the gravitational force

10. Gravity
the greater the distance between two objects, the smaller the gravitational force
the force of gravity decreases by the amount equal to one divided by the distance (d) squared
1/d2

11. What is air resistance? air resistance
force that opposes the movement of an object in air

12. Air Resistance
a larger surface area usually results in greater air resistance
lighter objects feel more air resistance than heavier objects

13. Terminal Velocity
speed at which air resistance and gravity acting on an object are equal
as an object falls, it’s speed increases at a steady rate until it reaches it’s terminal velocity

14. Vacuum – empty space
in a vacuum, all objects fall at the same speed

15. What is friction? Friction force that opposes the motion of an object
the force of friction works in the opposite direction of the force of motion

16. Types of Friction Sliding Friction
the source of friction is the contact between two surfaces, at least one of which is in motion

17. Types of Friction Air Resistance
friction results from air pushing on an object as it is moving

18. Types of Friction Rolling Friction
friction between two surfaces that are not in constant contact
ex. wheels

19. Types of Friction
Fluid friction – friction that occurs when an objects move through a fluid; through a gas or liquid

20. Types of Friction
Static friction – friction of an object at rest

21. Friction friction makes motion possible
friction also makes it hard to move objects
reducing friction makes it easier to move objects

22. How can friction be reduced?
by changing sliding friction into rolling friction
by using lubricants
Lubricants – substances that reduce friction