Scientific Terms Common Terms and Expressions Gravitational Force (Gravity) Pull of Earth Magnetic Force Magnetic pull; magnetic push Electrical Force (Electricity) Static cling; static electricity; force of an electric current; force of lightning Mechanical Force Muscular Force; hurricane force; slapshot; punch Frictional force (Friction) Rubbing; abrasion; roughness; force of resistance Tensile Force Tightening Compressive force Crush; squash; squeeze; press; pinch; grip Rotational Force Twist; turn, wring, coil, twirl All forces have 2 components: • Magnitude: the quantity of force • Direction: which way force is pushing/pulling Use arrows in diagrams • Top of arrow shows direction • Thickness shows magnitude Unit of measure = Newton (N) • Named after Sir Isaac Newton The forces Force applied to hold rock up. are equal in magnitude and opposite in direction. Force of gravity Mass is a measure of the amount of matter or material in an object. Weight is a measure of how strong the force of gravity is between two objects. Ifyou hold a rock in your hand, Earth pulls the rock toward its centre, and the rock pulls Earth toward its centre. However, the rock’s mass is so small in comparison to the mass of Earth that when you let go of the rock, the rock moves much farther toward Earth than Earth moves toward the rock. In fact, it looks as though only the rock moves. http://www.youtube.com/watch?v=grWG_U 4sgS8 Earthexerts a force of 9.8 N for every kilogram of an object’s mass The force of gravity is 9.8 N/kg The moon’s force of gravity is approx. 1/6 of Earth’s pull. So if you went to the moon, your mass would be the same but your weight would be 1/6 what it is now. To pick up something you must overcome the force of gravity that is keeping it where it is. How much force do you need to apply to pick up a container of milk? Ifa litre of milk has a mass of about 1kg You would have to lift upward with 9.8 N of force to pick it up! Input force Load force A spring scale is a device used to measure forces. The object to be weighed is attached to the end of a helical spring. How far the spring stretches (the tension on the spring) indicates the weight of the object The tension is shown on a calibrated scale on the side. Groupings: Pairs Using a spring scale, estimate and measure forces needed to perform common everyday tasks. Create the following chart: Task Estimated Actual Difference force Force Liftone of the standard masses in your hand and get a feel for how much force is needed to hold it up. Now, lift the mass with a spring scale and record the force in your chart. Repeat 2 – 3 times with different masses. APPROPRIATE Be sure to select the most spring scale. Now practice a simple task, such as lifting a pencil case, until you get a feel for the amount of force needed. Then estimate the amount of force needed to perform the task. Record the task, your estimate, and the actual force needed. Determine the difference. Repeat for 5 other common items (binder, water bottle, openning a drawer, etc.) You may need to use string to assist you. One per pair: Completed Chart: Be sure to include all the elements of a good data table Answers to Questions: 1.Why was it important to lift the standard masses and use the spring scale before making estimates? 2. Compare your early estimates with your last few. Which were more accurate?