18. a) The materials that are in contact. The two materials and the nature of their surfaces. ...
b) The force pushing the two surfaces together. Pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other.
19. the quantity of motion of a moving body, measured as a product of its mass and velocity.
20. According to Newton's third law of motion, action force is equal to reaction but acts on two different bodies and in opposite directions. When a horse pushes the ground, the ground reacts and exerts a force on the horse in the forward direction. This force is able to overcome friction force of the cart and it moves.
21. The mass of an object is a measure of the object's inertial property, or the amount of matter it contains. The weight of an object is a measure of the force exerted on the object by gravity, or the force needed to support it. The pull of gravity on the earth gives an object a downward acceleration of about 9.8 m/s2.
22. R12. Mass is more fundamental because it is an intrinsic property of an object. Weight varies with location depending upon the acceleration due to gravity eg. for a mass m = 10kg on Earth it`s weight is W = mg = 10 x 10 = 100N.
Cause their are both have difference s
Because they consume prey from all trophic levels beneath them.
The radius of the electron's or basically the energy level for which the electron is found orbiting the nucleus of he hydrogen atom, as the principal quantum number tells us primarily the energy level that the electron will be found, is it the 1st, 2nd, and 3rd. The other quantum numbers tells us more specifically as per the subshell of the main shell the electron is in, the spin of the electron etc.
Number 13 is D. Mendeleev. He was a Russian chemist and inventor who formulated the periodic table.
