Presentation on theme: "Speed is the rate that an object moves. (How fast something moves) Speed is measured in meters per second (m/s), kilometers per hour (km/hr) and miles."— Presentation transcript:
Speed is the rate that an object moves. (How fast something moves) Speed is measured in meters per second (m/s), kilometers per hour (km/hr) and miles per hour (mph) Speed is useful for knowing how fast vehicles move, how fast people run, etc Speed is calculated by dividing the distance traveled by the time it takes to travel the distance. Speed = distance / time S8P3a.Motion8/28/12 What are the similarities and differences between speed and velocity? Page 11
Velocity is the rate that an object moves in a particular direction. Velocity is measured in meters per second (m/s), Kilometers per hour (km/hr) and miles per hour (mph) with a direction. For example: 40 m/s west Velocity is useful for airplanes, helicopters and boats. Velocity is calculated by dividing the distance traveled by the time it takes to travel the distance. Velocity = distance / time SPEED AND VELOCITY ARE NOT THE SAME Page 13
On page 12 of your INB, make two columns and categorize the following descriptions as speed or velocity: SpeedVelocity car moving at 35mph bird flying at 40mph north jogger running at 10m/s jogger running at 10m/s south a vehicle racing at 125mph
Acceleration is the rate at which an object’s velocity changes. There are 3 ways that acceleration can occur: 1.speeding up (acceleration or positive acceleration) 2.slowing down (deceleration or negative acceleration) 3.Changing direction Acceleration is expressed in units like meters per second squared (m/s 2 ) The formula for calculating acceleration is: Average acceleration= final velocity-initial velocity time S8P3a.Motion9/5/12 What is the relationship between velocity and acceleration? Page 15 Summary
On the top half of pg.14 of your Science NoteBook Identify which is an example of acceleration and which is not: A train traveling 65 miles per hour north A boat sailing west at 5 knots A person jogging at 3 meters/second along a curved path A car stopped at a stop light A car stopping at a stop light A truck speeding up from 55mph to 75mph A person jogging at a constant speed along a straight path AccelerationNot Acceleration
On the bottom half of pg.14 of your Science NoteBook Complete the practice acceleration problems provided and paste into bottom half of page 14 leaving room for a summary.
On the top of pg.16 of your Science NoteBook Write the following standard neatly. S8P3b. Students will demonstrate the effect of balanced and unbalanced forces on an object in terms of gravity, inertia and friction
All motion is due to forces acting on objects. A force is a push or pull. Force is measured in a unit called Newtons (N). The net force is a total combination (sum) of all forces acting on an object. A balanced force is one in which the net forces equal zero. There is no motion. An unbalanced force has a net force greater than zero. The object acted on shows movement in one direction. Only an unbalanced force can change the motion of an object. S8P3b.Forces9/7/12 How are forces related to the motion of objects? Page 17
On the bottom of pg.16 of your Science NoteBook Underneath the standard
An unbalanced force acting on an object at rest will cause it to __________________. An unbalanced force that acts on an object already in motion can change the speed OR direction of an object. Unbalanced forces can act in the same direction or in opposite directions. If forces are in the same direction, you add them. If forces are acting in the opposite direction, you subtract them. S8P3b.Forces9/10/12 How are forces related to the motion of objects? Page 19 Summary
On pg.18 of your Science NoteBook During the game of tug-of-war What happens when the two teams pull with equal force? What type of forces are these called? How would you represent this with force arrows? What happens when one team pulls with a greater force? What type of forces are these called? How would you represent this with force arrows and an illustration?
There are many different types of forces in nature that act on objects. They include: gravity, friction and inertia. Gravity is an attractive force that works to pull objects together. The law of universal gravitation states that a force of gravity acts between all objects in the universe. There are two factors that affect the force of gravity between objects: 1. the objects’ masses and 2. the distance between them. (mass is the amount of matter in an object). S8P3b.Forces9/17/12 How are forces in nature related to the motion of objects? Page 21
The larger the mass, the more the gravitational attraction. The shorter the distance between the objects, the more the gravitational attraction. Inertia is the tendency of an object to resist a change in motion. Mass affects inertia. An object with a large mass has more inertia than an object with a small mass. S8P3b.Forces9/17/12 How are forces in nature related to the motion of objects? Page 23 Summary
Draw/write the following 3 questions and determine which has a greater gravitational “pull” and WHY. 1. 2. 3. On page 20 35kg25kg 5kg 25kg Set A (red balls) Set B (green balls)
Moon Gravity Actual Orbit Inertia Earth Gravity and inertia work together to keep the Moon orbiting Earth. First, the Moon’s inertia pushes it to travel continuously in a straight line. At the same time, Earth’s gravity is pulling the Moon toward Earth. These combined forces cause the Moon to move in a curved path (orbit) around Earth. Without gravity, the Moon would fly off into space. The Moon is able to continuously orbit Earth because the Moon’s inertia and the Earth’s gravity are balanced. On page 22
Question 1 What happens to the motion of an object when the forces are balanced? – A. The motion changes. – B. The motion does not change. – C. The motion speeds up. – D. The motion slows down.
Question 2 What happens to an object if the forces acting upon it are unbalanced? – A. Its motion will not change. – B. The motion will come to a stop. – C. The net force will be zero. – D. Its motion will change.
Question 3 What happens to an object moving in the same direction as the net force? – A. It will speed up. – B. Its motion will not change. – C. It will stop moving. – D. It will slow down.
Question 4 Which pair of objects will have the greatest gravitational attraction to each other? – A. two cinder blocks 6 centimeters apart – B. two marbles 12 centimeters apart – C. a cinder block and marble 6 centimeters apart – D. a cinder block and marble 12 centimeters apart
S8P3b. Laws of Motion 9/19/12 Since gravity works to pull objects toward each other, what keeps the planets from crashing into the Sun? Page 25 Summary Newton’s first law of motion states that an objects at rest will stay at rest, and an object in motion will continue in motion in a straight line unless an unbalanced force acts on the object. This law is sometimes called the Law of Inertia. This means if the net force acting on an object is zero, the object remains at rest, or if the object is already moving, continues to move in a straight line with constant speed.
S8P3b.9/19/12 If Newton’s first law of motion is accurate, why do moving objects sometimes come to a stop? Page 27 The force that brings nearly everything to a stop is called friction. Friction is the force that opposes the motion of an object. This contact force acts whenever an object in motion rubs against a surface. Friction opposes motion when two surfaces touch. The contact reduces the speed of the moving object and releases heat. There are 3 types of friction: sliding friction, rolling friction and static friction Laws of Motion
S8P3b.9/20/12 If Newton’s first law of motion is accurate, why do moving objects sometimes come to a stop? Page 29 Summary Sliding friction is friction that slows down an object that slides. Example: brake pads on a bicycle that rub against the wheel Static friction is friction that acts on an object at rest. Example: trying to move a refrigerator Rolling friction is friction that acts when an object rolls across a surface. Example: rolling a cart around Laws of Motion
Draw an illustration of friction in action. Your illustration must be neat and colored. You must identify the two surfaces that are interacting and what is occurring in order for it to be friction. You must also identify the type of friction. On page 26
Identify an example of each type of friction (not those provided in class). Illustrate, color and label the friction interaction of each using the table format below. On page 28 Type of FrictionExampleIllustration with Labels
S8P3b.9/25/12 What is the relationship between force, mass and acceleration? Page 31 Summary Newton’s laws Newton’s second law of motion states that the acceleration of an object depends on the mass of the object and the amount of force applied. This law can be expressed mathematically with: Force = mass x acceleration (newton) = (kilogram) x (meters/second 2 )
Write the question and answer: Name two ways to increase the acceleration of an object. 1. 2. What force is necessary to accelerate a 1,250kg car at a rate of 40m/s 2 ? On page 30
S8P3b.9/25/12 When a person pushes on a wall, the wall pushes back. How does this relate to Newton’s 3 rd law? Page 33 Summary Newton’s third law of motion states that for every action there is an opposite and equal reaction. Forces act in equal and opposite pairs. Example: pushing on a wall, a rocket launching, diving off the side of a pool. Laws of Motion
S8P3c.9/27/12 What is a simple machine and how do they make work easier? Page 35 Work is the application of a force to an object to move a certain distance in the direction of the force. Work requires two things: a force applied to an object the object must move in the direction of the force. Example: pushing a lawnmower The equation for work is: work = force x distance The unit for work is the Joule (J). Simple Machines
S8P3c.9/27/12 What is a simple machine and how do they make work easier? Page 37 A simple machine is a device that makes work easier by changing the size of a force OR changing the direction of a force. The six simple machines are: Pulley Inclined plane Wedge Wheel and Axle Screw Lever Simple Machines Summary
An inclined plane is a straight, slanted surface. They make work easier because it is easier to push an object up a ramp than to lift the same object straight up to the same height. Ex. a ramp On page 34
A wedge is an inclined plane that is wider or thicker at one end than at the other. A wedge makes work easier because when moved, a wedge is used to cut, split, or pry apart objects. Ex. knife blade or axe. On page 34
A screw is an inclined plane that is wrapped around a cylinder. When a screw is turned, a small force is applied over the long distance of the screw’s threads. On page 34
A lever is a simple machine that consists of a bar that pivots at a fixed point called a fulcrum. The force applied to a lever is called the effort. The object being moved is called a load. There are three classes of levers: 1 st class, 2 nd class and 3 rd class. On page 36
A wheel and axle is a simple machine that consists of a shaft called the axle, inside the middle of a wheel. Ex. bicycle wheel Any force that is applied to the wheel gets transferred to the axle and vice versa. When force is applied to the wheel, the difference in size between the wheel and axle causes the force to increase as it is transferred to the axle. On page 38
A pulley is a rope or chain wrapped around a wheel. A load is attached to one end of the rope. A force is applied to the other end of the rope. There are 2 kinds of pulleys: fixed and movable. A fixed pulley is one that does not move. They are often used to lift something. A fixed pulley changes the direction of force, but does not reduce the amount of force needed to lift the load. On pages 38-39
A movable pulley is a pulley that moves. One end of the rope is tied to a stationary object and the other is free for you to pull on. The load is attached directly to the pulley. The pulley moves along the rope as the free end is pulled. They reduce the amount of force needed to move an object, but you must pull the rope farther. On pages 38-39
A block and tackle is a system (combination) of pulleys. On pages 38-39
Mechanical advantage = output force (Newtons) input force (Newtons) MA = F out F in Efficiency = output work (joules) X 100% input work (joules) Eff = W out X 100% W in On pages 38-39