FORCE & MOTION
I. Force A. Def. – a push or pull B. Measured in Newtons (n) – by a spring scale
C. Forces in combination 1. same direction 50N 50N = 100N 2. opposite direction 100N 25N=75N
D. Friction – force that slows or prevents motion 1. Sources a. roughness of surface; ex. road, floor b. Weight (forces pushing surfaces together); large object has more friction
2. Types a. static friction – friction at rest; ex. eraser sits still b. sliding friction – something pushed across a surface; ex. box pushed on floor
c. rolling friction – between wheels & floor; ex. car d. fluid friction – friction of liquids or gases; ex. airplane, boat
3. reducing friction a. lubricants – oil, wax, grease b. switch from sliding to rolling c. smooth surface – ex. use sandpaper
4. increasing friction – make surfaces rougher & increase the weight (forces pushing the surfaces together
Why did the teacher insist that her students wear rain slickers? She wanted to reduce the friction between them.
E. Gravitational Force – force of attraction between any 2 objects that have mass (Newton) 1. Law of universal gravitation – all matter experiences gravity; the size of the force depends on the masses of the objects & the distance between them
a. size: sunearthmoon (tides) b. distance – earth’s gravity affects us more because we are closer 2. weight – measure of gravitational force
Gravity – 2:34
F. Centripetal Force – force which pulls objects toward the center of a curving path
II. Motion – occurs when an object changes position over time A. Types of Motion 1. neither direction nor speed changes 2. accelerating/decelerating 3. when force applied
4. opposite forces 5. vertical 6. circular 7. projectile
B. Motion described 1. relative position to a reference point; ex. moving past the middle school, comet moved past the sun 2. Energy- Law of conservation of energy: energy is neither created nor destroyed; a. potential – stored energy; ex. car @ top of hill b. kinetic – energy in motion; ex. car moving
3. direction – N, S, E, W 4. speed – rate at which object moves over time
a.) speed = distance/time ex. 100 km/2 sec. = 50 km/sec b.) time = distance/speed ex. 100 km/ 50 km/sec = 2 sec. c.) distance = speed x time ex. 50 km/sec x 2 sec = 100 km
What is meant by unbalanced force? *If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion. * If they are not equal and opposite, then the forces are unbalanced and the motion of the object changes.
Some Examples from Real Life A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion. Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.