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Investigating how the strength of a force changes as you move further away.
Have you ever noticed that a magnet can 'snap' a paperclip from an inch away, but does absolutely nothing if it's across the room? Why does this invisible power seem to vanish as you move away?
Magnets are amazing because they have an invisible force. This means they can push or pull objects without even touching them! This area of invisible power around a magnet is called a magnetic field. However, this power doesn't go on forever. Think of a magnet like a campfire: if you stand right next to it, you feel a lot of heat. If you walk to the other side of the park, you won't feel the heat at all. Magnetic force works the same way. The distance, or the amount of space between the magnet and the object, determines how much 'tug' the object feels.
Quick Check
If you move a magnet closer to a refrigerator, does the pull get stronger or weaker?
Answer
The pull gets stronger.
To understand forces, scientists use measurement. We can use a ruler to find the exact moment the magnetic force wins the 'tug-of-war' against friction and gravity. When you slowly slide a magnet toward a paperclip, there is a specific distance where the clip will suddenly jump or 'snap' to the magnet. If the clip is at cm, nothing might happen. But at cm, it flies through the air! This tells us that the strength of the force is tied directly to how many centimeters are between the two objects.
Let's see how distance affects a small magnet: 1. Place a paperclip at the cm mark on a ruler. 2. Place a magnet at the cm mark. 3. Slowly slide the magnet toward the clip: cm... cm... cm... 4. At cm, the paperclip jumps! 5. The 'Maximum Attraction Distance' for this magnet is cm.
Quick Check
If a paperclip jumps at cm, is that magnet stronger or weaker than a magnet that only makes it jump at cm?
Answer
It is stronger because it can pull from a further distance.
This isn't just a 'magnet rule'—it is a rule for almost all invisible forces in the universe! Whether it is the static electricity that makes your hair stand up or the gravity that keeps the moon near Earth, distance is the boss. As the distance increases, the force decreases. In Grade 3, we just need to remember: More Space = Less Force. If you want a force to be stronger, you have to close the gap. This is why you have to get a magnet very close to a heavy object to lift it, but a light object might jump from further away.
Imagine you have two magnets taped together. 1. With one magnet, the paperclip jumps at cm. 2. With two magnets, the force is doubled. 3. You predict the clip will jump from further away because the force is stronger. 4. You test it and find the clip now jumps at cm!
Does the force change if something is in the way? 1. Place a piece of cardboard between a magnet and a paperclip. 2. The cardboard adds cm of distance. 3. Because the magnet is now cm further away from the clip, the pull will feel weaker than if the cardboard wasn't there at all.
What happens to the strength of a magnet's pull as you move it further away from a metal object?
If Magnet A picks up a clip from cm and Magnet B picks up a clip from cm, which magnet is stronger?
True or False: A magnet must be touching a paperclip to exert a force on it.
Review Tomorrow
Tomorrow, try to explain to a friend why a magnet can't pick up a spoon from across the kitchen table using the word 'distance'.
Practice Activity
Find a magnet at home and a ruler. See which object in your house has the longest 'snap point' distance!