Block 1: General Physics. Chapter 1: Making Measurements

Transcription

1 Chapter 1: Making Measurements Make measurements of length, volume, and time. Increase precision of measurements. Determine densities of solids and liquids Rulers and measuring cylinders are used to measure length and volume Clocks and electronic timers are used to measure intervals of time. Density is calculated from mass and volume measurements Measurements of small quantities can be improved using special instruments (vernier calipers) Length base unit is meter 1 m = 100 cm 1cm = 10 mm Volume base unit is liter 1 L = 1000 ml 1 ml = 1 cm 3 Base unit is second 1 sec = 1000 ms 60 sec = 1 min 3600 sec = 1 hour An INTERVAL is the difference between the start and stop time (we don t always start at 0!) D = m/v Mass 1 kg = 1000 g Volume can be measured using a cylinder, by displacement for a solid, and by a ruler (lxwxh) for a regular solid. Measurements of small quantities can be improved by making multiple measurements. Measuring a stack of paper and dividing by number of sheets. Measuring several periods of a pendulum and dividing by number of periods (swings).

2 Chapter 2: Describing Motion Interpret distance against time and speed against time graphs Calculate speed and distance Calculate acceleration Average speed is the distance travelled in a specific time interval Speed equals the gradient of a distance time graph Distance equals total path traveled on a distance time graph Distance equals the area under the speed time graph Acceleration is the change in speed in a specific time interval Acceleration equals the gradient of a speed time graph Speed = distance/time (s = d/t) Distance = speed x time (d = s x t) Time = distance/speed (t = d/s) Base unit is meters/sec (m/s) 1 km = 1000 m Gradient = slope (it s a British thing) Positive slope = moving away from start Negative slope = moving towards start Horizontal line (0 slope) = not moving Add the absolute values of all the distances on the graph Calculate distance travelled by breaking the graph into rectangles and triangles and calculate the area (b x h or 1/2bh for triangle) Acceleration = speed /time (a = s/t) Unit is m/s 2 Positive slope = increasing speed Negative slope = decreasing speed Horizontal line (0 slope) = CONSTANT SPEED

3 Chapter 3: Forces and Motion Identify forces acting on an object Describe how a resultant (net) force changes the motion of an object Describe the relationship between force, mass, and acceleration Explain the difference between mass and weight Describe the effect of drag on a moving object Calculate the resultant of two or more vectors A force is a push or a pull. Forces are vectors they have direction. Forces cause objects to accelerate. The greater the mass of an object, the smaller the acceleration caused by a given force Unit: Newton N 1 N = 1kgm/s 2 You must assign a positive and negative direction when adding forces F = ma (Newton s second law) a = F/m and m = F/a Forces cause objects to speed up, slow down, or turn. The resultant force is the single force that has the same effect as two or more forces added together Mass is the amount of matter in an object. Weight is the force of gravity on an object s mass. Friction and drag (air resistance) are forces that act in the direction opposite of motion. W = mg Unit is Newtons N g = 10 m/s 2 acceleration of gravity Use the Pythagorean theorem to add forces acting at right angles. c 2 = a 2 + b 2

4 Chapter 4: Turning Effects of Forces Describe the turning effect of a force Determine if an object is in equilibrium Calculate moments, forces, and distances Understand center of mass and stability Moment of a force = force x perpendicular distance from pivot to force Moment = F x d Moments can be clockwise or counterclockwise Forces acting through the pivot DO NOT create a moment Equilibrium: The resultant force is zero and the resultant moment is zero Center of Mass Stability Find the center of mass of a lamina Total clockwise moment = Total counterclockwise moment Point on an object where if all of the objects mass was concentrated at a single. A force acting through the center of mass does not cause a moment. Card and string lab. A string hanging from any point on a lamina will pass through the center of mass. Hang the mass from different points, and the intersection is the center of mass.

5 Chapter 5: Forces and Matter Identify how forces change the shape of objects Interpret extension load graphs Apply Hooke s Law of Springs Understand the factors that affect pressure Calculate pressure Forces can change the shape of matter The extension of a spring is equal to the stretched length minus the original length. The force stretching a spring is called the load. Hooke s Law states the extension of a spring is directly proportional to the load (force) applied as long as the limit of proportionality is not exceeded (over stretched). Pressure is the force per unit area acting on an surface x = stretched length unstretched length F = kx x = extension in m or cm k = spring contsant (N/m or N/cm) p = F/A (F can be a force on an object or the weight of an object) Unit is Pascals (Pa) = 1 N/m 2 Pressure in fluids is proportional to the density of the fluid and the height of the fluid column Pressure can be decreased by increasing the surface area. p= ρgh ρ= density (kg/m 2 ) g = 10 m/s 2 h = height of fluid column (m)

6 Chapter 6: Energy Transforms and Energy Transfers Chapter 7: Energy Resources Identify forms of energy Describe energy conversions Apply the principle of conservation of energy Explain and calculate energy efficiency Calculate potential and kinetic energy Identify energy resources (CH 7) Energy can be associated with an object (stores) or moved from one place to another (transfers) The unit of Energy is the Joule (J) = 1 Nm Law of conservation of energy The efficiency of an energy conversion is the fraction of energy that ends up in the desired form. Gravitational Potential Energy depends on the weight of the object and height above the ground. Kinetic Energy is depends on an objects mass and speed (velocity) All energy on Earth originates from the Sun. Energy resources can be classified as renewable or non-renewable Stores: Kinetic energy, gravitational potential energy, chemical energy, nuclear energy, strain (spring) energy, internal energy. Transfers: Electrical energy, thermal (heat) energy, light energy, sound energy. In any energy conversion, the total amount of energy before and after the conversion is constant. Calculating percent efficiency %Eff = (energy out/energy in) x 100% GPE = mgh or GPE = Wh (W = weight) m = mass (kg) g = 10 m/s 2 h = height (m) KE = ½ mv 2 m = mass (kg) v = speed or velocity Renewable resources can be easily replaced (solar, biomass, wind). Nonrenewable can be used up (fossil fuels, nuclear power)

7 Chapter 8: Work and Power Skill Goal: Explain the concept of work and power Calculate work and power Work and Energy are related by the workenergy principle Work is equal to the force applied in the same direction as the distance the object moves. The joule is the unit of both work and energy Power is the rate energy is transferred, or the rate work is done. Energy is the ability to do work. Work done = Energy added W = F x d the units are Joules (J) = Nm 1 joule (J) is equal to the work done by a force of 1 N when it moves through a distance of 1 meter. P = ΔW/t unit is Watts (W) = J/s P = ΔE/t Δ = final initial (change)