UNIT 2 FORCE & MOTION

Motion Objects move in a variety of ways! How do we know when an object is moving? Constant motion - an object covering equal distances in equal amounts of time: constant speed Non-constant motion - an object doesn’t cover equal distances in equal intervals of time An object is moving if its position changes; does the background change? Speed describes how fast an object moves. FORCE & MOTION

What is Speed? Speed measures motion. To determine speed you must Measure the distance traveled by an object Measure the time it takes to travel that distance FORCE & MOTION

Determining Speed? Don’t forget to use International Scientific Units or SI units! How fast an object moves in meters per second (m/s) “rate of motion.” A change in position from one place to another in any direction is described as motion. (meters or kilometers) The length of time that it takes for that change to occur, or the rate of change in position is described as speed. (seconds or hours) FORCE & MOTION

Types of Speed Average speed – distance covered by an object divided by the time it takes to travel that distance Instantaneous speed – speed measured at any given instant Constant speed – when speed doesn’t vary over a long period of time Negative acceleration – slowing down Positive acceleration – speeding up Resting objects - speed of 0 m/s FORCE & MOTION

Speed & Velocity SPEED – how fast an object moves VELOCITY – describes both speed and direction d s t Speed =d/t Define and practice and more Velocity practice Define and practice - http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L1d.html Velocity practice is http://library.thinkquest.org/10796/ch2/ch2.htm FORCE & MOTION

Velocity example FORCE & MOTION

Velocity example FORCE & MOTION

Momentum Moving objects have momentum Momentum depends on both its velocity and its mass Momentum has direction; an objects momentum is in the same direction as its velocity If a train and a car are moving at the same velocity, which one has the greater momentum? FORCE & MOTION

Measuring Momentum The more mass an object has, the greater its momentum (for a given velocity) The faster an object is moving, the greater its momentum Momentum is zero if an object isn’t moving SI unit is kilograms times meters per second (kg*m/s) FORCE & MOTION

Momentum Equation For momentum momentum = mass x velocity p = m*v p Definition Youtube spaceship battle (Can’t see at school) Definition - http://id.mind.net/~zona/mstm/physics/mechanics/momentum/definition/mome ntumDefinition1.html Youtube spaceship battle -http://www.youtube.com/watch?v=GihlZ0Mnq-k FORCE & MOTION

Momentum example FORCE & MOTION

Momentum example FORCE & MOTION

Momentum example FORCE & MOTION

Acceleration The rate at which velocity changes –not speed! When an object speeds up then acceleration is in the same direction as velocity. When an object slows then acceleration is in the opposite direction as that of velocity. FORCE & MOTION

Car acceleration Press on the gas – car speeds up – acceleration is in the direction of the car’s motion Press on the brake – car slows down – acceleration is opposite to the car’s direction Turn the steering wheel – changes velocity even if speed doesn’t change – acceleration changes FORCE & MOTION

Acceleration formula Acceleration = change in velocity/time v a t Change in velocity = final velocity – initial velocity v = vF - vI a = v/t FORCE & MOTION

Acceleration example FORCE & MOTION

Practice Acceleration definition and practice Line Rider 2 Definition from Physics Textbook Notes and practice Acceleration def and practice- http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L1e.html Line Rider 2 -http://www.official-linerider.com/play.html Def from Physics text - http://www.hypertextbook.com/physics/mechanics/acceleration/ Notes and practice - http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Kinematics/Acceler ation.html FORCE & MOTION

Force A force can most easily be described as a push or a pull. When a force is applied to an object, the velocity of that object changes. This change in velocity constitutes an acceleration. So, forces are tied to accelerations. FORCE & MOTION

Force Net force – combination of all of the forces acting on an object, determines whether the velocity of the object will change An object accelerates in the direction of the net force; kicking a ball Balanced forces completely cancel each other and the combined force equals zero; tug-of-war where rope doesn’t move Force and Motion Experiments Force = f mass * acceleration m a Force and Motion Experiments - http://wings.avkids.com/Curriculums/Forces_Motion/index.html FORCE & MOTION

Force - Balanced Forces on an object that are equal in size and opposite in direction are balanced forces and will not change the velocity of an object FORCE & MOTION

Force - Unbalanced When the forces become unbalanced the NET FORCE applied to the object will always change the velocity of the object by changing its speed or direction. FORCE & MOTION

Friction Friction is a force that opposes motion between two surfaces that touch. The amount of friction depends on the kinds of surfaces and the forces pressing the surfaces together. FORCE & MOTION

Friction If a ball is rolling across the floor, it will slow and stop. Force keeps the ball rolling and FRICTION is the unbalanced force acting against the ball’s direction of motion. Friction affects non-moving objects. Friction of brakes balances the force of gravity and stops a parked truck from rolling down a hill. Try walking on ice and on grass. You slip on ice because there is less friction between your shoes and the ground. FORCE & MOTION

Friction (rolling, sliding,fluid) Sliding friction is the strongest motion friction. Ex: push a box across the floor. Rolling is used to reduce sliding friction. Ex: wheels Fluid friction is from fluid or gas. It reduces air resistance. Oil reduces sliding friction. Ex: WD40 on a door hinge FORCE & MOTION

Air resistance Another type of friction The amount of air resistance on an object depends on its size and shape as well as on the speed with which it moves. Objects with larger surfaces have greater air resistance. Air resistance also increases as the objects speed increases. FORCE & MOTION

Gravity Gravity is a force. Every object in the Universe exerts a force of gravity on every other object. The amount of gravity depends on mass and distance. The more mass an object has and the closer the distance to another object the more gravitational force. Gravity website and games Gravity website and games - http://www.sciencemonster.com/gravity_inertia.html FORCE & MOTION

Gravity Example FORCE & MOTION

Weight The measure of the force of gravity on an object is the object’s weight. Weight refers to gravitational force between earth and a body at Earth’s surface. If a person weighs 100 pounds the Earth’s gravity is exerting 100 pounds of force on that person. The moon has a weaker gravitational force than the Earth because it doesn’t have the mass of the Earth. FORCE & MOTION

Weight formula Weight = mass * gravity w m g Gravity = 9.8 m/s2 Weight is measured in Newtons w m g FORCE & MOTION

Free fall Caused by gravity Objects experience air resistance which is fluid friction Acceleration due to gravity is 9.8 m/s2 FORCE & MOTION

Newton’s Three Laws Cool website 1st Law -An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called "the law of inertia". 2nd Law -Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). 3rd Law -For every action there is an equal and opposite re-action. Cool website - http://teachertech.rice.edu/Participants/louviere/Newton/index.html FORCE & MOTION

Remember the Laws? 1st Law 2nd Law 3rd Law FORCE & MOTION Demonstration FORCE & MOTION

Newton’s Laws of Motion Definition Simplified NASA site to visit Explanation Demonstrations Detailed information Definition - http://www.school-for-champions.com/science/motionlaws.htm Simplified - http://www.allworldknowledge.com/newton/ NASA site to visit - http://www.lerc.nasa.gov/WWW/K-12/airplane/newton.html Explanation - http://www.physicsclassroom.com/Class/newtlaws/newtltoc.html Demonstrations - http://www.physicsclassroom.com/mmedia/newtlaws/newtlawsTOC.html Detailed information - http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/newtltoc.html Brainpop - http://www.brainpop.com/science/motionsandforces/newtonslawsofmotion/ subscription site FORCE & MOTION