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Transcript

MAY THE FORCE BE WITH YOU… What is a force? FORCE = Any push or pull which causes something to move or change its speed or direction BALANCED VS. UNBALANCED FORCES Balanced forces are equal in size and opposite in direction. There is NO motion. Unbalanced forces are not equal in size and/or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results. They change the speed and /or direction of an object. BALANCED FORCES • If forces on an object ARE equal in size, the object will not move or change speed. • When forces ARE equal, the object will not change direction. UNBALANCED FORCES • If forces on an object ARE NOT equal, the object can move or change speed. • When forces ARE NOT equal, the object can change direction. GIVE EXAMPLES OF FORCES Balanced Forces? Unbalanced Forces? ENERGY AND MOTION • Mechanical energy is the energy an object has because of motion or its position. • There are two kinds of mechanical energy: potential and kinetic. Potential Energy Potential energy is energy an object has because of its mass or position. This cat has potential energy because of his mass and height above the ground. How could we increase the cat’s potential energy? Kinetic Energy Kinetic energy is the energy an object has because it is moving. The greater the speed and the mass of the object, the greater its kinetic energy. WHAT IS MOTION? A change in position of an object compared to a reference point. Motion involves all of the following: speed, velocity, acceleration, and de-acceleration. WHAT IS SPEED? The rate of change in position Speed = distance ÷ time WHAT IS VELOCITY? Speed plus direction Example: 50 km/hour north WHAT IS ACCELERATION? The rate of change in velocity. Positive acceleration = speeding up Negative acceleration = slowing down (decelerate) WHAT IS GRAVITY? The force of attraction between objects that have mass. All objects have mass, so gravity acts on all objects. Greater mass = stronger force of gravity. Why is the gravity on earth more than gravity on the WHAT IS FRICTION? The force that opposes motion between two surfaces in contact with each other. Examples: Your hands rubbing together, air slowing down a floating feather, water slowing down a boat. WHAT IS INERTIA? The tendency of a body to resist a change in motion. An object at rest stays at rest. An object in motion stays in motion…unless acted on by an outside force. Click here to learn more about Speed is the distance traveled in a unit of time. Velocity is speed in a direction. Speed is how fast an object is moving. Speed = distance time Your Turn! : Calculate the speed of the toy car over a distance of 2 meters. The graph shows the movement of a car over time. What is the car’s average speed? A.10 km/hr B. 15 km/hr C. 30 km/hr D. 60 km/hr A foam dart is thrown toward a dartboard. The graph represents its motion. At about what speed is the dart traveling when it hits the dartboard at 3 meters from the starting point? A.7.0 m/s B.8.5 m/s C.8. 75 m/s D.9.0 m/s SOURCES • http://www.openclipart.org/detail/38293 • http://carpictures.cc/cars/photo/car_model/24574/BM W_F3 • http://ritter.tea.state.tx.us/student.assessment/resource s/online/2009/taks_g08_science/8Science.htm • http://images.google.com/imgres?imgurl=http://www.ka renelkan.com • http://oncegray.files.wordpress.com/2009/10/yoda.jpg