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Is gravity real or does the Earth just suck? New End Primary School Tuesday 31st March Aristotle: for an object to continue moving there must be a force acting on it. It is understandable that he thought this was the case: In the seventeenth century Galileo argued that objects keep moving unless acted on by a force, for example friction. NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH It’s easy for us to imagine a situation where there is no friction. If Aristotle had been right, this would happen… Newton later said: Objects continue to move in a state of constant velocity unless acted upon by an external net force. 1ST LAW. Newton Astronauts need to beware! Newton Newton also said: “Every action has an equal and opposite reaction.” - His 3rd law. Which explains why guns recoil and how rocket engines work. PUSH PULL TWIST NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH move faster move slower change shape stop acceleration moving NEW END PRIMARY SCHOOL start moving change direction TUESDAY 31ST MARCH NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH FORCE measured in NEWTONS NEW END PRIMARY SCHOOL Weight of an apple ≈ 1 Newton TUESDAY 31ST MARCH Force of Floor acting on Box Force from floor on box cancels gravity. If the floor vanished, the box would begin to fall. Force of Earth acting on Box (weight) NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH Try to suck the ball through the straw Straw Ping-pong ball NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH The arrow represents the force of gravity NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH FORCES ARE BALANCED To stop gravity, we need an upward force. FORCES ARE NOT BALANCED The ball does not fall when…. ACCELERATION We can draw this by having arrows of the same weight. NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH THRUST FRICTION AIR RESISTANCE NEW END PRIMARY SCHOOL GRAVITY TUESDAY 31ST MARCH For example What happens when when a driver there who aretravelling is unbalanced at constant forces acting speed on an object? accelerates or puts on the brakes. Accelerate: drive Brake: drag Speed decreases until Speed drag increases until drag matches drive again. grows to match drive. GRAVITY LIFT FRICTION AIR RESISTANCE MAGNETISM UPTHRUST THRUST NEW END PRIMARY SCHOOL ELECTRICITY TUESDAY 31ST MARCH 1. When Isaac Newton discovered gravity, what knocked the sense in to him? 2. Which force keeps us on the Earth? Try sucking up the different balls with a straw. 3. Thurst is a powerful force that moves things forward. Which machines rely on clever design and thrust to keep them in the sky? Can you find any in the class room? Try throwing the machines! Who can get them furthest? 4. When two magnetic objects are bought near each other, they can attract or repel. Can you find any magnetic objects in the room? 5. Compasses work based on magnetism- they feel the magnetic field of the Earth. Point your compass to North! 6. When items move across rough surfaces, they lose energy and slow down due to friction. Try and find something that would cause a car to feel friction. 7. When objects fall to the ground they slow down due to air resistance. What do you think would have lots of air resistance? 8. When we turn a light switch, little electrons carry forces which cause material in the light bulb to heat up and emit light. Find where you think there is electricity in the room! NEW END PRIMARY SCHOOL TUESDAY 31ST MARCH