Resumen de materia de science, para 3 grado de primaria

Science

1. WHAT IS A FORCE ? I s a push or a pull that moves an object PULL! PUSH!

2. Characteristics of Forces Can change the direction or speed of a moving object. 2. Can change the shape of an object. 3. N o t all forces need contact between objects. Examples: magnetic force and Earth’s gravity.

3. Push or Pull?

4. Balance and Unbalanced Forces Balanced forces Unbalanced forces Balanced forces happen when two or more forces push or pull on an object equally . As a result t he object does not move , or it keeps moving at the same speed and in the same direction. Unbalanced forces happen when one force is stronger than the other. As a result t he object moves, speeds up, slows down, or changes direction .

5. Gravity Is the force that pulls an object toward the center of Earth .

6. Characteristics of gravity Gravity is a force. → It is a “pull” that makes things move toward each other. Gravity pulls everything toward Earth. → That’s why apples fall down, not up! Gravity makes things fall. → If you drop a toy, gravity pulls it to the ground. Gravity keeps us on Earth. → Without gravity, we would float into space. Gravity works on everything. → Big or small, heavy or light — all things have gravity acting on them. The more mass, the stronger the pull → Earth is big, so its gravity is strong. That’s why the Moon orbits Earth We measure the force of gravity in newtons (N)

7. HOW DO WE MEASURE FORCE? A FORCE METER measures how much force you need to move an object. Weight

8. FRICTION Definition Is a force of resistance that happens between objects that are in contact with each other . Uses Helps us walk and run safely without slipping. Helps vehicles stop (brakes use friction). Helps objects stay in place (like a book on a table). Helps us hold things (like a pencil or a cup).

9. LIGHT Transparency means how much light can pass through a material . It tells us if we can see through something .

10. Types of transparency Transparent – Light can pass . You can see clearly through it . Example: Glass window, clear water, plastic wrap. Translucent – Some light can pass . You can see light through it , but not clearly . Example: Frosted glass, thin paper, diamonds, ice, tissue paper. Opaque – Light cannot pass . You cannot see through it at all . Example: Wood, metal, a book cover, cardboard boxes.

11. WHAT ARE SHADOWS? A shadow is a dark shape made when something blocks light . Shadows have the same shape as the object that blocks the light. Shadows need light to appear.

12. HOW SHADOWS ARE MADE? Light shines on an object. The object blocks some of the light . A dark shape (shadow) appears on the surface behind the object.

13. SHADOWS Shadows can be big (object close to light) or small (object far from light) depending on how close the object is to the light. (Distance) Shadows move when the light moves . You can make shadow puppets with your hands!

14. WHAT IS A MAGNET? Is a piece of metal, or a rock that contains metal, that attracks other metals . Natural Artificial Minerals like iron ore Cobalt , nickel

15. MAGNETS Magnetism is the force of a magnet . It works over distance , so a magnet can attract or pull toward it , a magnetic object or another magnet without touching it .

16. WHAT ARE THEY USED FOR? Holding things in place Example: Refrigerator door to stay closed or magnets holding notes or drawings. Finding metal objects Example: Magnets can pick up pins, nails, or paperclips. In electronics (make vibrations, store information) Example: Magnets are inside speakers, phones, and computers. In compasses Magnets help a compass show directions . Separating metals Example: Magnets help separate metal from trash in recycling plants Modern means of transportation Example: modern trains have no wheels, instead they float on a magnetic track