## Monday, June 21, 2010

### Forces

What is a force?

A force is a push or pull that one object exerts on another.
It produces or tends to produce motion, and stops or tends to stop motion.

Types of forces (7 types):

1. Contact Force - push experienced by two objects pressed together.
2. Weight - gravitational pull of the earth on an object
3. Friction - motion opposing force that exsit when surface of two objects move
against each other.
4. Tension - pull at both ends of a sting, spring or rope
5. Resistance - a type of force existing in fluids giving a viscous effect
See website for general information:
(http://www.millersville.edu/~jdooley/macro/derive/viscous/visplat/visplat.htm)
6. Electric Force - push or pull between electric charges
7. Magnetic Force - push or pull between magnets or magnets and magnetic materials

S.I. unit of force is newtons(N)

1N - amount of gravitational force acting on 100g mass
1N is defined as a force that produces acceleration of (1m/s)/s on a mass of 1kg

Activity:

Object Melon Apple Pat Eatladee Fred

Mass (kg) 1 kg Ans(b) 25 kg Ans(c)

Weight (N) Ans(a) 0.98 N Ans(d) 980 N

(a)9.8 N (or ~10 N if approximating g to be 10 m/s/s)
(b)0.1 kg (or ~0.098 kg if approximating g to be 10 m/s/s)
(c)245 N (or ~250 N if approximating g to be 10 m/s/s)
(d)100 kg (or ~98 kg if approximating g to be 10 m/s/s)

2. Different masses are hung on a spring scale calibrated in Newtons.

1. The force exerted by gravity on 1 kg = 9.8 N.
2. The force exerted by gravity on 5 kg = ______ N.
3. The force exerted by gravity on _______ kg = 98 N.
4. The force exerted by gravity on 70 kg = ________ N.