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Transcript
Name_______________________________ period _________ date _____________ Study guide for Chapter 2 Test: Forces Force A push or pull, some are contact forces (pushing a cart) and others are non-contact forces (electric force, magnetic force, gravity) Newton Abbreviation is N, the unit used to measure force, named after Isaac Newton. Net Force The combination of all the forces acting on an object, the TOTAL force on an object. Balanced Forces (Explain what they are and what effect they have on an object’s motion.) When all the forces on an object cancel each other out. Balanced forces do NOT cause a change in motion. If an object was still, it stays still with balanced forces. If the object was moving and the forces become balanced, the object keeps moving at a constant speed and direction. Unbalanced Forces (Explain what they are and what effect they have on an object’s motion) When the forces on an object are unequal. Unbalanced forces DO cause a change in motion. Unbalanced forces cause an object to accelerate (speed up, slow down, or change direction) Name_______________________________ period _________ date _____________ Terminal velocity (Explain what it is and what has to happen to the forces on an object to obtain terminal velocity) The top speed an object reaches when being pulled downward by gravity. It occurs when gravity and air resistance (fluid friction) equal each other. When terminal velocity is reached, acceleration is at zero. Inertia The tendency (habit) of matter to resista a change of motion. It takes an unbalanced force to cause an object to change its motion and overcome inertia. An example would be when your car suddenly stops, your body moves forward until your seatbelt stops you. Friction (Explain what it is, why it happens, and how to increase or reduce friction) The force that opposes or resists motion. It occurs because surfaces are never completely smooth and the surfaces “catch” on each other. One thing that affects friction is force between objects and as it increases, friction increases. Another factor that influences friction is surface area, and as it increases, friction increases. The third factor that influences friction is surface substance, and as it increases (or gets rougher), friction increases. Four types of friction and examples: Static: When an object is resisting motion, and not yet moving. Name_______________________________ period _________ date _____________ Ex. Pushing a heavy piece of furniture. Sliding: When 2 solids slide past each other. Ex. Sliding down a slide at the playground, erasing pencil marks. Rolling: When one of the objects is round Ex. Wheels of any type, rollers in a factory, ball bearings Fluid: (Make sure you know that both liquids and gases are fluids.) When one of the substances is a fluid. Ex. Swimming, air resistance when biking The two factors that affect gravity and how they affect gravity: One thing that affects gravity is distance and as it increases, gravity decreases. The other factor that influences gravity is mass , and as it increases, gravity increases. Newton’s 3 Laws of Motion (Define and be able to apply all three laws to real life events.) 1st law: An object in motion will stay in motion and an object at rest will stay at rest until acted upon by an unbalanced force. It takes an unbalanced force to overcome inertia and make an object accelerate (speed up, slow down, change direction) 2nd law: The acceleration of an object depends on the force applied to the object and the mass of the object. Name_______________________________ period _________ date _____________ If the mass of an object increased, but the force on it stayed constant then the acceleration of the object would decrease. o Ex: If a car and truck were racing but both have the same engine, the car will have more acceleration and win. If the force on an object increased, but the mass of the object stayed the same then the acceleration would increase. o Ex. If I push my sister on the swings soft vs. hard, the stronger push will accelerate her more. If the mass doubled and the force was cut in half, then the acceleration would be reduced to ¼ o Example: If I push a cart filled with 2x the groceries, but have a child (smaller, weaker) push it with ½ my force and the cart will accelerate only ¼ as much. 3rd law: For every action there is an equal and opposite reaction. ***Action/Reaction forces do NOT act on the same object. They are not balanced forces, because they act on separate objects.*** If an action force was wind pushing/pulling on a windmill The reaction force would be the windmill pushing/pulling on the wind (air molecules) The result of the action force would be: The windmill starts to turn The result of the reaction force would be: The air molecules slow down when they hit the windmill. Name_______________________________ period _________ date _____________ Motion Study Guide o position - location of an object. For example the watch is on the dresser. The dresser is the location. o motion - an item's change in position. o scalar - number that represents one term of movement such as speed. Does not represent speed and direction. For example, 55 MPH is a scalar quantity. o vector - has magnitude and direction. Would represent speed and direction. For instance, 55 MPH South is a vector quantity. o speed - scalar quantity. Measures only rate of motion. o velocity - vector quantity. Measures speed and direction. o acceleration - vector quantity. Name given to a result of change in speed, direction or both. An example of acceleration would be when a car speeds up or turns a corner. Defined as the time rate of change. Formulas for Motion o Speed formula: average speed = distance traveled/time to travel distance (Average speed equals distance traveled divided by time to travel distance). The answer will list a number to represent speed as well as which types of units were measured for amount of distance traveled as well as amount of time it took to travel the distance. For example if the answer is measured in meters per second the answer and the number for the answer is two, then the answer will look like this -- 2 m/s. o Velocity formula: If the motion is constant and in one direction, the speed formula is used and the direction is written and understood as well as the speed. Using the example above for instance, the answer is two miles per second or 2 m/s, but now you need to include the direction. If the movement is North the answer would read 2 m/s N or 2 m/s north. o Acceleration formula: average acceleration = change in velocity/time for change to occur. Using constant acceleration, the answer is written as m/s2 (meters divided by seconds squared).