Transcript Magnetism
Magnetism 4th grade Science What is a magnet? Any object with magnetic force Magnetic Poles • The parts of a magnet where the magnetic force is strongest • All magnets have two poles- a north and a south pole • When two magnets come together, a north and south pole attract each other • “Like” poles (north-north or southsouth) repel each other Magnetic Force The force that pushes magnets apart or pulls them together • Magnets that are far apart do not push or pull enough to move each other. • The magnetic force between two magnets is weak when magnets are far apart. • The magnetic force gets stronger as the magnets are brought closer together. What kinds of materials are attracted to magnets? What kinds of materials are not attracted to magnets? Let’s see...Conduct Investigation! Magnetic Field The area of magnetic force around a magnet • This is how a magnet can attract or repel objects without touching them. • Every magnet has a magnetic field around it. • The magnetic field is strongest near the magnet’s poles. The magnetic field is weakest farther away from the poles. Did you know? • Our planet is a giant magnet. Much of the Earth is made of iron which creates a magnetic field that surround Earth. • Long ago people noticed one end of a magnet pointed north so they called it the “north-seeking end”. The same happened with the “south-seeking end”. It was shortened to north and south poles of a magnet. Drawing Conclusions Investigation Teacher demonstration… Why does this happen? Michael Faraday and Joseph Henry in 1820s and 1830s •Made amazing discoveries about electric currents and magnets •They found that electric currents make magnetic fields and that magnets could generate an electric current. What is an electromagnet? A magnet formed when electric current flows through wire wrapped in coils around an iron bar How does an electromagnet work? •When an electric current flows through the coil, it creates a magnetic field. •This magnetic field causes particles inside the metal coil to line up. •The metal core becomes magnetic. •When the current stops, the metal core is no longer magnetic. Let’s try it! Build an electromagnet... Materials: power source (battery), 1 piece of wire (50 cm in length), nail Investigation: 1. Wind the wire around a nail 20 times. 2. Attach the wire ends to the battery. 3. Test it!