Force and Motion

Potential vs. Kinetic Potential Kinetic * GPE * KE * stored energy * energy of motion * not moving * moving * the higher the object * the faster an object the more PE the more KE * GPE=mgh * KE=mv2 G= 9.8 m/s2

Mechanical vs. Chemical Mechanical Chemical ME = PE+KE Physical change * Chemical change Only changes the physical * changes the appearance composition Ex. Gears moving in a car * Ex. food being broken down Energy that is moving * energy that is stored

Sample Question A 21.7 kg ball is located on a shelf 1.6 m above the ground. Which best describes the energy of the ball? Its energy is lost once it falls off the shelf Its energy depends upon the speed the ball will travel It has mechanical energy in the form of potential energy It has mechanical energy in the form of kinetic energy

Sample Question What happened to the ball’s energy from Point 1 to Point 4? Stored Energy was transformed into energy of motion Energy of motion was transformed into chemical energy Stored energy in the ball applied a force to get the ball to move Internal energy caused the ball to move until the energy was gone

Sample Question As a roller coaster car travels down a hill, which type of change in energy allows it to speed up? A. Potential energy changing into heat energy B. Potential energy changing into kinetic energy C. Kinetic energy changing into heat energy D. Kinetic energy changing into potential energy

Types of Energy Electrical: energy that is transferred by electrical charges or current Sound: associated with vibrations of matter and requires an object to travel through (Medium). Ex. Water Solar: the energy given off by the sun Chemical: energy that is stored in the chemical composition of matter Thermal: the energy given off by heat Light: energy given off by light Nuclear: the potential energy stored in the nucleus of an atom

Sample Question What form of energy does a car’s engine convert into mechanical energy? Light Wind Chemical Gravitational

Sample Question Which type of energy is changed by plants into chemical energy? A. Solar B. Nuclear C. Thermal D. Gravitational

Simple Machines Type Definition Example Illustration Lever   Inclined Plane Pulley Wheel & Axle Wedge Screw A solid bar that rotates around a fulcrum Wheelbarrow Handicap ramp A flat horizontal or sloped ramp Crane, gears A wheel that turns on an axle Car or gears A wheel that is fixed to a pulley 2 incline planes that are together screwdriver Spiral stairs or meat grinder An incline plane wrapped around a shaft

Sample Question How can an inclined plane make work easier? By increasing the amount of friction necessary for the task By increasing the effort necessary to raise an object By decreasing the effort required to raise an object By decreasing the efficiency of the task

Sample Question Which simple machine would be the most efficient for lifting an object 30m off the ground? Pulley Screw Wedge Lever

Force and Motion Important Terms Position: location (can be an object or place) Reference Point: location that you compare your object or place’s position Motion: change of position over time

Forces and Motion Terms Speed: the measure that something moves in a given amount of time speed=distance/time Velocity: speed in a specific direction velocity=distance/time Acceleration: the rate at which velocity changes with time acceleration=velocity final- velocity initial/time

Force and Motion Important Terms Friction: force that resists the motion between two surfaces in contact. Force: a push or pull (F= M x A) Balanced force: net force is zero, the motion of an object does not change Unbalanced force: changes the motion of an object Inertia: the resistance of an object to a change in the speed or direction of its motion

Newton’s 1st Law of Motion An object at rest stays at rest, and an object in motion stays in motion at the same velocity, unless acted upon by an unbalanced force. Newton’s First Law is also called the Law of Inertia. Inertia is closely related to mass. When you measure the mass of an object, you are also measuring its inertia. The more mass something has, the harder it is to change its motion. Ex: It’s easier to stop an empty wagon than a wagon full of sand.

2nd Law of Motion Acceleration of an object increases with increased force and decreases with increased mass. The direction in which an object accelerates is the same as the direction of the force. Simply put: Newton’s Second Law is… F = ma (Force = mass x acceleration) The standard unit of force is the newton (N). Because force = mass x acceleration, force is measured in units of mass (kg) times units of acceleration (m/s2). A newton is the amount of force that it takes to accelerate 1 kg of mass 1 m/s2. So…. I N = 1 kg x 1 m/s2.

Sample Question John wants to build a racetrack that will allow his toy cars to travel fast when force is applied. Which material should be use? carpet, because friction will be high Gravel, because friction will be high Plastic, because friction will be low Sandpaper, because friction will be low

3rd Law of Motion Forces always act in pairs! Newton’s Third Law: For every action, there is an equal and opposite reaction. Every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back on the first object.

Sample Question A magnet is placed near a pile of steel paper clips. Which will most likely occur? The magnet will provide a balanced force, causing the paper clips to spin in circles. The magnet will provide an unbalanced forces, keeping the paper clips stationary. The magnet will provide a balanced force, pushing the paper clips away from it. The magnet will provide an unbalanced force, pulling the paper clips toward it.

Summary of Newton’s 3 Laws

Distance/Time Graphs The motion of an object can be represented in a line graph. The data table below charts the motion of an object in 20 seconds. Construct a line graph on page 28 (blank page) that shows the motion of the object. Be sure to label both axes. Then, use the graph to describe the motion of the object between 0 and 10 seconds. Distance vs. Time Time (s) Distance (m) 5 10 15 20

Sample Question Which describes their motion? Steven threw four balls into the air and recorded their heights. The chart below shows the maximum height for each ball. Ball P went twice as high as Ball N Ball M went twice as high as Ball N Ball P went two meters higher than Ball O Ball N went two meters higher than Ball O Ball Maximum Height (m) M 2.0 N 1.5 O 4.2 P 3.0

Sample Question The chart shows the distance traveled by an object over 100 seconds. What happened to the motion of the object between t=50s and t=70s? The object increased its speed The object decreased its speed The object stopped moving The object changed directions

Sample Question Which graph represents a moving object with a constant speed throughout its entire travel time?