FORCE AND MOTION Study Notes FORCE: a push or pull acting on an object. examples of forces are gravity, friction, magnetism, and applied forces. Forces cause an object to change its speed, direction, or both. Applied force: is force that a person or thing applies to another object. There are BALANCED and UNBALANCED Forces: Balanced forces are forces acting on an object from opposite directions that are equal. These objects with balanced forces acting upon them will most likely be STILL – Not Moving. Unbalanced forces are forces acting on an object from opposite directions that are not equal. These objects with unbalanced forces acting upon them are in MOTION - MOVING. The Tug-Of-War in the top image is a “draw” – no one is winning or losing – BALANCED FORCES The Tug-Of-War in the bottom image shows the Left side winning because they have more force than the right side – UNBALANCED FORCES INERTIA: is the “stubbornness” of an object to a) stay at rest, b) stay in motion, or c) stay moving in one direction. Law: Nothing moves from sitting, stops from moving, or changes direction without an outside force acting on it. (Newton’s 1st Law of Motion; “Law of Inertia”) GRAVITY: is the force that pulls everything toward the center of the earth. In the Catapult Lab we conducted, we flung objects of different masses but applied the same strength of force by pulling back the spoon the same for each clay object. And we found that objects of small mass were less affected by Gravity and that allowed those to fly faster and further than objects with greater mass. The greater the mass, the more gravity (and air resistance – a type of friction) affected their speed and distance – the greater the mass, the slower and they flew and the closer they landed. GRAVITY affects objects being thrown in the air – and the relationship with the object and the ground is affected by the gravity and mass of the object: FRICTION: is a force that works against motion; the action of one surface or object rubbing against another surface or object. Friction stops or slows down moving objects. Friction can help moving objects change direction. Air Resistance is a type of friction. It slows things down that are moving through the air (cars, thrown objects, falling objects). MOMENTUM: officially, momentum is the amount of mass an object has multiplied by its velocity. Mass x Velocity For 5th grade purpose, let’s just say that MOMENTUM is the force of energy an object has when it is moving. You need to know that the larger the mass of an object in motion, the more momentum it will have than objects with smaller mass. But only true if the velocities of the two objects are similar. And, similarly, the more velocity an object has in motion, the more momentum it will have than objects with less velocity. But only true if the mass of the two objects are similar. If a baseball is thrown and travels at 55 mph, And a large truck is also traveling at 55 mph, ….the truck with much more mass will have much more MOMENTUM….and it will take much more energy to stop the truck than it will to stop the baseball. An object in motion has INERTIA – it’s moving and wants to continue moving! And it has MOMENTUM (force is needed against its movement to stop the object). The larger the mass, the harder it is to stop it because it will have more momentum than a lighter object. SPEED: calculated by this: Distance divided by time SPEED = distance / time SPEED = distance ÷ time A familiar example is the speed of a car. In the U.S., this is usually expressed in miles per hour. Think about a trip you and your family made in the car. Maybe the trip covered 120 miles and it took 3 hours. What was the car’s average speed? Speed = distance / time Speed = 120 miles / 3 hours = 40 mph On the basketball court we walked fast from start to finish and most of you walked an average of 88 feet in 11 seconds. So, to calculate the speed, we plug in the numbers to the SPEED FORMULA: SPEED = distance / time SPEED = 88 feet / 11 seconds = 88 ÷ 11 = 8! But you need to include a label with that number 8 ….. well, we walked 88 feet in 11 seconds, so the feet and the seconds are part of the label. If we walked 88 feet in 11 seconds, then we walked 8 feet in 1 second, right? We use the word “per” to mean “in one”…..8 feet per second = 8 feet in one second SO……. SPEED = 88 feet / 11 seconds = 88 ÷ 11 = 8 feet per second, or 8 ft/sec ALSO – You need to know how to calculate DISTANCE when given Time and Speed: Just like 50 = 100 ÷ 2 2 x 50 = 100 Speed = Distance ÷ Time Time x Speed = Distance So, if you’re given the Speed and Time, then you can calculate the Distance traveled! Examples: If you travel for 1 hour at 30 mph (miles per hour)…then you traveled 30 miles! Because…1 hour x 30 = 30 If you travel for 2 hours at 30 mph….then you traveled 60 miles! Because…2 hours x 30 = 60 If you travel for 3 hours at 40 mph = 3 x 40 = 120 miles you traveled! GRAPHING Graphing Distance and Time We spent time looking at numerous graphs and matching them with stories and tables of data. We found that the appearance or shape of the graph does NOT represent the shape of the path or ground. (in red – there are 3 LINE SEGMENTS above) Like in this graph above…. We found that the “up and down” of the line on the graph indicates the DISTANCE from home – the higher the coordinate, the further away from home. When the coordinate is on the bottom line, then the traveler is “home.” We found that the steeper the line segment, the faster the speed. If the line segment is closer to a straight line, that means the traveler is going slower. If the line segment is a straight line, then the traveler has completely stopped.
