Forces

Essential Questions What is a force? What are the different kinds of forces? What is friction? How can friction be increased or decreased?

For 800 years the Leaning Tower of Pisa has been tilted. Located in Italy, officials worried that it would fall over. What forces are acting on the Leaning Tower of Pisa?

Forces When you jump up in the air, what pulls you back down to Earth? What pulls a magnet together or pushes it apart? The answer is…. Forces

A FORCE is a push or pull that causes changes in motion. Forces A FORCE is a push or pull that causes changes in motion.

Forces can affect motion in several ways: → They can make objects start moving. → They can make objects move faster. → They can make objects move slower. → They can make objects stop moving. → They can make objects change direction.

Forces Nothing can change position, speed, or direction unless a force acts on it. A book doesn’t just fall off of a table by itself. A force has to push it! Think about this how do you get your backpack on your back? You have to lift it and pull it onto your shoulder. Without a force, your backpack can’t move!!

Measuring Forces Forces are measured in Newtons (N) Forces are measured using a spring scale.

Types of Forces Friction Gravity Magnetic

Friction When a soccer ball is kicked across the grass, it eventually slows down. Why? FRICTION Friction is a force that works against motion Friction can make things slow down or stop, or it can keep things from moving at all.

Erasable Friction When you use an eraser, you are creating friction as your eraser touches the paper.

More About Friction Friction is greater between rough surfaces than between smooth ones. Ice skaters glide along the ice because there is little friction between the blades and the ice.

Heat it Up! Rub your hands together for a minute. You feel heat! This is because you are creating friction between your hands.

Friction If you pour oil onto a wooden surface, its friction would be reduced. This is because it makes the surface slippery.

Let’s Review Oreo likes to race small toy cars. He wants to race them on a surface that will let the cars go further faster. What kind of surface would you suggest? Why?

Let’s Review The bike tires felt hot from __________ after the boy skidded. A. magnetism B. gravity C. friction C.

A. friction B. gravitation C. inertia D. magnetism A. Mr. Gates mops the gymnasium floor every day. When he finishes mopping, he puts up the sign shown below. The effect of which force is weakened when the floor is wet? A. friction B. gravitation C. inertia D. magnetism A.

Let’s Review A puck slides along an icy surface. What makes it slow down? A. It runs out of push B. It rubs against the ice C. It runs out of electricity B.

Let’s Review A boy sits halfway down a grassy slope. What keeps him from sliding? A. Weight B. Gravity C. Friction C.

Let’s Review Which of the following is an example of trying to increase the friction? A. Squirting oil in hinges B. Spreading grit on icy roads C. Waxing the underneath of skis B.

Let’s Review A. On which surface will a toy car travel the farthest? A. Ice B. Wood C. Carpet A.

Let’s Review B. Which of the following is NOT true? A. Friction can only slow things down B. Friction is never useful C. Friction can stop things from moving B.