2. All About Forces and Gravity
Chapter 18 FORCES
All About Forces and Gravity

3. # Vocabulary
1.  force:  a push or pull that may cause an object to move, stop, or change direction
2.  friction:  a force that opposes motion
3.  gravity;   the force of attraction between objects
4.  gravitational force:  the pull of all objects in the universe on one another
5.  magnetic:  having the property of attracting iron objects
6.  magnetic force:  the force produced by a magnet

4. Lesson 1: What Forces affect objects on earth every day?

5. forces A force is a push or a pull that may cause changes in motion.
Nothing changes its position, speed, or direction unless a force acts on it.
Brainpop Forces

6. friction Friction is a force that works against motion.
Friction can make things slow down or stop, or can keep things from moving at all.
Friction can also make heat.

8. Gravity Brain pop Gravity is the attraction between you and Earth.
Gravity causes falling objects to speed up as they fall.
Objects move faster, or ACCELERATE, as they fall.
The speed of any falling object is about 10 m/sec after the first second. After the next second, it is 20 m/sec. After the third second, it falls at about 30 m/sec. Turn to your shoulder partner and discuss what is happening.

9. Magnetic force brainpop - magnetism
An object that attracts iron is a magnet.
The force of the magnet is called its magnetic force.
The magnet is surrounded by a force field called the magnetic field.
A magnet has 2 ends, called poles marked north and south.

10. Lesson 2 what are balanced and unbalanced forces?

11. Vocabulary # 7-10
Balanced forces: forces that act on an object but cancel out each other
unbalanced forces: forces that act on an object and don’t cancel out each other, unbalanced forces cause a change in motion.
Net force: the combination of all the forces acting on an object
Buoyant force: the upward force exerted on an object by water

12. Balanced and unbalanced forces
Forces that act on an object but cancel each other are called balanced forces.
WHEN UNBALANCED FORCES ACT ON AN OBJECT, MOTION CHANGES. THE OBJECT MAY START, SPEED UP, SLOW DOWN, STOP, OR CHANGE ITS DIRECTION.

13. Net Force
The combination of all the forces acting on an object is called the net force.
When forces are balanced, the net force is zero.

14. To calculate net force:
Assign a plus (+) to the forces acting in one direction. Forces acting in the opposite direction get a minus (-). Add the strengths of the forces to get the net force.

15. Buoyant force Buoyant force is the upward force of water on an object.
Buoyant force acts in the opposite direction from weight, and helps the object float.
If the BF is equal to or greater than the weight, the object floats.
If the weight is greater than the BF, the object sinks.

16. Lesson 3: What is work, and how is it measured?

17. Vocabulary #11-17 Copy into journal
work: the use of a force to move an object through a distance
Simple machine: a device that makes a task easier changing the size or direction of a force or the distance over which the force acts
Lever: a bar that makes it easier to move things
Fulcrum: the balance point on a lever that supports the arm but does not move
Wheel-and-axle: a wheel with a rod, or axle, in the center
Pulley: a wheel with a rope that lets you change the direction in which you move an object
Inclined plane: a ramp or another sloping surface

18. Work Brainpop
Work is using a force to move an object through a distance.
Work is measured in units called joules.
A medium-size apple
weighs about 1 N.
If you lift the apple 1 m,
you do 1 J of work.

19. Machines and work
Remember, machines don’t actually reduce the amount of work.
A simple machine is a tool that makes a task easier by changing the strength or direction of a force or the distance over which the force acts.

20. Compound machines
Compound machines are made up of 2 or more simple machines.
Watch the video and takes notes in your journal – I will check on Monday!
Bill Nye – Simple Machines video