FORCE & MOTION

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 50 N  50N  = _____N 2. opposite direction 100 N  25 N  = ____ N

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

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

FRICTION

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 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

Alien Song

a. size: sun  earth  moon (tides) b. distance – earth’s gravity affects us more b/c we are closer 2. weight – measure of gravitational force

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 2. Energy- Law of conservation of energy: energy is neither created nor destroyed; a. potential – stored energy; ex. top of hill b. kinetic – energy in motion; ex. car moving

Kinetic & Potential Energy – 2:56

3. direction – N, S, E, W 4. speed – rate at which object moves over time

a.) speed = distance/time ex. 100 miles/2 hrs. = 50 miles/hr b.) time = distance/speed ex. 100 miles/ 50 miles/hr = 2 hrs. c.) distance = speed x time ex. 50 miles/hr x 2 hrs. = 100 miles

C. Newton’s 3 Laws of Motion 1. Newton’s 1 st Law of Motion (Law of Inertia) – an object at rest or in motion tends to stay at rest or in motion unless acted on by a force (INERTIA) ex.

Seatbelts

Newton’s 1 st law of Motion – force, friction, & Inertia – 6:04

2. Newton’s 2 nd Law Motion – the change in motion depends on the mass of the object & the amount of force applied; (a = F/m) OR the amount of force depends on the mass times the acceleration (F = m x a); Ex.

Newton’s 2 nd Law – 2:34

3. Newton’s 3 rd Law of Motion – for every force action, there is an equal & opposite force reaction (action- reaction) Ex. bike hits car, car hits bike;

Springboard

Newton’s 3 rd Law of Motion – 3:00

D. Momentum – measure of how hard it is to stop an object; - Law of Conservation of Momentum – the total momentum of objects that collide with each other is the same before & after the collision

THE END!!