Newtonian Mechanics

Question 1

Force

Answer 1

Vector quantity describing the push/ pull on an object with units: Newton
F = ma

Question 2

Newton

Answer 2

N = kg m/ s^2

Question 3

Mass

Answer 3

Scalar quantity that measures an object’s inertia.

Question 4

Weight

Answer 4

A force that involves the gravitational pull of an object. W = mg

Question 5

Center of Gravity

Answer 5

The point where the entire force can be thought to be applied that is usually the geometric center for a homogenous body.

Question 6

Newton’s First Law

Answer 6

A body at rest or in motion with constant velocity will remain that way unless a net force acts upon it

Question 7

Newton’s Second Law

Answer 7

Σ F = ma
The forces can also be broken up into its components
When Σ F = 0, then a = 0

Question 8

Newton’s Third Law

Answer 8

Fa = - Fb

Question 9

Why would it be safer to collide with bales of hay than with a solid fence?

Answer 9

It takes more time for a vehicle to slow down when colliding with a bale of hay, leading to a smaller average impact force.

Question 10

Normal Force

Answer 10

The perpendicular component of a force, where N = mg on a flat plane and N = mg sin θ on an incline.

Question 11

Friction Force

Answer 11

Antagonistic force dependent upon the objects involved, where F = μN

Question 12

How do you calculate the forces acting upon a block sliding on a frictionless incline?

Answer 12

1. Draw a free-body diagram (the block feels two forces: gravity and the normal force)
2. Assign x and y axes (preferably make x parallel to the incline)
3. Find the components of the forces (Wx = mg sin θ and Wy = mg cos θ, because the angle of incline equals the angle between the gravitational force and the normal force)
4. Only the forces in the x-direction affect the motion of the block, since there is no acceleration in the y direction (recall that x is parallel to the incline) [ΣFx = Wx = max and ΣFy = N - Wy = may = 0] {apply Newton’s second law separately to each direction}
5. The length of the incline can be found with d = v0t + (at^2)/2
6. The vertical height of the incline can be found with sin θ = h/d

Question 13

Gravity

Answer 13

The attractive force felt by all forms of matter: F = Gm1m2/ r^2
G = 6.67 X 10^-11 N m^2/kg^2
r = distance between the centers of the masses

Question 14

Equilibrium

Answer 14

When ΣF = 0

Question 15

Translational Equilibrium

Answer 15

ΣFx = 0 and ΣFy = 0

Question 16

How do you calculate the forces acting upon a mass being held by a number of strings in equilibrium?

Answer 16

1. Draw a free-body diagram at the point of intersection, do not forget to include weight. The tension in the vertical component should be equal to the weight of the mass, because ΣFx = 0 and ΣFy = 0.
2. ΣFx = 0 = ΣT cos θ
3. ΣFy = 0 = ΣT sin θ - W
4. Substitute into the equations as necessary

Question 17

Rotational Equilibrium

Answer 17

Rotational equilibrium depends on force magnitude, force direction, and the distance from the force to the axis of rotation. The greater the distance, the greater the change in rotational motion. Clockwise is negative and anti-clockwise is positive: Στ = 0

Question 18

Torque

Answer 18

τ = rF sin θ, with SI units N m

Question 19

How do you calculate the forces with a balanced see-saw?

Answer 19

1. Take the point of the fulcrum as the pivot point to eliminate the normal force and weight of the see-saw from the equation because r = 0.
2. Στ = 0 = Σmgd, because θ = 90 on a perpendicular see-saw
3. N exerted by the fulcrum is equal to the sum of all weights acting on the see-saw

Question 20

Translational Motion

Answer 20

Motion where there is no rotation

Question 21

Static Friction

Answer 21

The force that must be overcome to set an object in motion.

Question 22

How is the magnitude of the acceleration for blocks connected by a string related?

Answer 22

The magnitude of accleration for the blocks should be the same

Question 23

Centripetal Acceleration

Answer 23

a = v^2/ r, pointed towards the center of motion

Question 24

What assumptions can be made when working with uniform circular motion?

Answer 24

Object speed is constant and there is no tangential acceleration.

Question 25

Centripetal Force

Answer 25

F = mv^2/ r