FORCES

1. FORCES Lesson 1: What Forces Affect Objects on Earth Every Day? Lesson 2: What are Balanced and Unbalanced Forces? Lesson 3: What is Work and How is it Measured?

2. Lesson 1 Vocabulary • Force- a push or pull that may cause an object to move, stop, or change direction • Friction- a force that opposes motion • Gravity- the force of attraction between objects • Gravitational force- the pull of all objects in the universe on one another • Magnetic- having the property of attracting iron objects • Magnetic force- the force produced by a magnet

3. A force is a push or pull that causes motion. Many different forces are pushing you and pulling you all the time. A force can speed things up, slow them down, or make them change their direction. Lesson One:

4. When skates did into the ice, the skater slows down. The force that makes things slow down is friction. Friction can stop something or keep it from moving at all. Friction can also make heat. Friction is greater between rough surfaces than it is between smooth surfaces. Lesson One:

5. The force of attraction between two objects is called gravity. All objects have some gravity. Larger objects have more gravity than smaller objects do. When you fall out of your chair, Earth’s gravity is what pulls you to the ground. Lesson One:

6. All objects in the universe, large and small, pull at one another. This pulling is called gravitational force. The strength of this force depends on two things. One is the distance between the objects( the force is stronger when they are near each other). The other factor is the mass of the objects, or the amount of matter (the force is stronger when they have more mass). Lesson One:

7. A person will weigh more on Earth than on the moon. The person’s mass remains the same, but the weight changes. This is because the weight is a measure of the amount of gravitational force pulling on an object. The fellow to the right weight 200 lbs on Earth but only 33 lbs on the Moon. Lesson One:

8. If you have ever picked up paper clips with a magnet, you might know the force produced in order to pick them up is magnetic force. A magnet is surrounded by a magnetic field that attracts objects. A magnet has 2 ends, called poles. The magnetic field is strongest at the poles. Earth is like a big magnet and its poles are called the North and South Poles. Lesson One:

9. Lesson 2 Vocabulary • 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 • Net force- the combination of all the forces acting on an object • Buoyant force- the upward force exerted on an object by water

10. Usually more than one force is acting on an object. When you go down a slide, gravity and friction are both acting on you. When the force of gravity and friction are equal, you stop because the forces cancel each other out. When forces act on an object and cancel each other out they are called balanced forces. Lesson Two:

11. Lesson Two: • If you give yourself a push going down the slide, you start moving again. • The forces become unbalanced forces. • In this game of Tug of War below, the forces are unbalanced. The team on the left is winning because they are pulling at the rope with more force

12. Remember that many forces are acting on an object at all times. All these forces together is the net force. Net force affects how the object moves. Lesson Two:

13. When you are in the water, you seem to weight less. This is because a force called buoyant force acts on your body. A buoyant force acts in the opposite direction of your weight. The buoyant force pushes you up so you seem to weigh less. Lesson Two:

14. Lesson 3 Vocabulary • Work- the use of a force to move an object through a distance • Simple machine- a device that makes a task easier by 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

15. In science, work has a special meaning. To do work, you must use a force to move an object. Pushing a box across the floor is work. Lifting a bucket is work. Doing a math problem in your head is not work. Lesson Three:

16. Lesson Three: • A machine is something that makes work easier. • This means you can do more work with less force. • A simple machine can change the size or direction of the force, or it can change the distance the object travels.

17. A lever is a simple machine. It is a bar that makes things move easier. A lever has 2 parts. The fulcrum is the balance point that supports the bar. Lesson Three:

18. An inclined plane is also a simple machine. It is a sloping surface, like a ramp. You use less force, but you go a longer distance. Lesson Three:

19. Another kind of simple machine is a pulley. A pulley is a wheel with a groove for a rope. A pulley can help you lift a heavy object. It lets you pull on the rope instead of pushing up on the object. Lesson Three:

20. A wheel and axle is a simple machine made of a wheel and rod. The rod (axle) goes through the center or the wheel. A doorknob is a wheel and axle. Lesson Three:

21. A compound machine is made up of 2 or more simple machines. It also makes work easier. One type of compound machine is a can opener which has a wedge that cuts the can and also a wheel and axle that you turn. Lesson Three: