Eighth Grade Science Midterm Study Guide Know the steps of the scientific method: Purpose, Research, Hypothesis, Experiment, Analysis, Conclusion (Purple cubs have exciting amazing cubs) Independent variable – is the one condition that you change in an experiment Dependent variable – the the variable that is changed because of the independent variable . Metric system: You will also have a few problems on SI- Metric System King Henry Died Unusually Drinking Chocolate Milk Kilo____ Hecto_____ Deca____ unit____ deci____ centi____ milli_____ Liter -­‐-­‐-­‐ Meter -­‐-­‐-­‐-­‐-­‐ Gram Samples: 600 mm = _____ m 0.35 liters = _____mL 1,050 g = _____kg 80 cm = _____m 1 L = _____mL 1 kg = _____ g 1.Average Speed = divide the total distance by the total time. Ex: 45km + 15 km = 60 km (total distance) 3 hr + 2 hr = 5 hr (total time) 60 km 5 hr = 12 km/h 2.Instantaneous Speed - the rate at which an object is moving at a given instant of time. 3.Velocity – speed in a given direction The velocity of an object gives both speed and direction. 4.The rate at which on object moves is called speed. An object is in motion only if its distance from a reference point is changing. In a circular motion, velocity of an object is constantly changing. The distance traveled by an object in a unit of time is called speed. Acceleration is the rate of change in velocity The object or point from which movement is determined is frame of reference. You can measure motion using distance, time and speed. Acceleration is the rate of change in velocity When doing motion problems please show the formula. (Use the Triangle) Speed = s = d/t Time = t = d/s Distance = d= t X s Velocity = v= d/t Time = t= d/v Distance d=t X s Average Speed = divide the total distance by the total time. Sample problem: What is the acceleration of an object that takes 20 sec to change from a speed of 200m/sec to 300m/sec? A = 300 – 200 20 = 100/ 20 = 5m/s Acceleration = FinalVelocity - InitialVelocity / Time An object or point from which movement is determined is called frame of reference. Scalars are quantities that are one dimensional like speed, time, distance etc. Vectors are quantities that have two dimensions such as velocity (speed and direction) Friction – To move an object you must exert a force that is larger than the force of friction Friction increases is surfaces push lightly against each other Smooth have less fricition Rough surfaces have more friction 4 kinds of friction: Static –the friction that acts on objects that are not moving Sliding – two solid objects slide over each other Rolling - when an object rolls across a surface. It is easier to overcome than sliding fricition Fluid – fluids such as water oil or air are materials that flow easily. Fluid friction occurs when a solid object moves through a friction ( know examples of each) Gravity – a force that pulls objects toward each other. Universal gravitation – the force of gravity acts between all objects in the universe. Two objects in the universe, without exception, attract ech other. Forces affecting gravity and gravitational attraction between objects – mass and distance. Weight – is the measure of the force of gravity on an object at the surface of a planet. Mass the amount of matter in an object. Laws of Motion: a. Newton’s First law of Motion: Law of Inertia. Object in motion stays in motion or an object at rest stays at rest UNLESS acted on by a FORCE. b. Newton’s Second law of Motion: F=ma. Force equals the product of an object’s mass and acceleration. (or Acceleration is equal to the force and inversely proportional to mass) c. Newton’s Third law of Motion: Action/Reaction Law. For every action there is an equal and opposite reaction. 2. Give an example for each of Newton’s laws a. Newton’s First law of Motion: bolder won’t move unless something pushes on it, and the moon won’t stop rotating unless a force acts on it. b. Newton’s Second law of Motion it takes more force to accelerate a school bus than a toy car. c. Newton’s Third law of Motion: my foot pushed on the ball (action force), the ball pushes back (reaction force) and fly’s forward (resulting net force). OR you sitting in the desk is pushing down on the desk and the desk is pushing up on you but they are balanced so no CHANGE in motion. Work is done on an object when the object moves in the same direction in which the force is exerted. To do work on an object, the object must move some distance as a result of your force. If the object does not move, no work is done, no matter how much force is exerted. The amount of work done on an object can be determined by multiplying force times distance. Work = Force x Distance One joule is the amount of work you do when you exert a force of 1 newton to move an object the distance of 1 meter. Power equals the amount of work done on a object in a unit of time. Power = Work Time Be able to do math problems for motion, acceleration work and power. Any material after Work and Power will not be included in the midterm exam.