Abeka Physics Section 9.1 Flashcards
Describe force
> force has same directions as the motion it produces
>force is vector quantity (has magnitude and direction)
Describe a free-body diagram
> in study of forces acting on a body, the body is often drawn in isolation from all other bodies
shows all of the forces acting on a body
same rules for drawing vector diagrams apply to drawing free-body diagrams
Which direction does acceleration move and at what rate? Explain why.
> A body will accelerate in the same direction as the net force acting upon it
at a rate given by Newton’s second law, F=ma, where F is the magnitude of the net force
a body will only accelerate if Sigma F does not equal zero
A man in trying to move a box. In the first situation, the man uses 10lb. of force to push the box. In the second situation, the man uses 10lb. of force to pull the box. Describe this.
> both efforts accelerate the box at exactly the same rate
State the principle of transmissibility
> “a force may be applied anywhere along its line of action without changing it effect”
Describe the unidirectionality of flexible ties
> force transmitted by a rope must be directed along the line of the rope (true for any flexible tie)
imagine that a rope is cast from a boat to a man on shore. If the man begins to pull on the rope, the force he exerts has no effect other than to cause motion in his direction.
Describe tension
> when string is fully stretched, the force is transmitted along the string to the hook without any reduction in strength
applied force pulls the first particle away from the second, but the two particles are held together by a force of attraction. As the distance between the two particles increases, the attractive (or restorative) force increases until it balances the applied force. Now, the force pulling the second particle toward the first is greater than the force pulling the second particle toward the third. As a result, the second and third particles move apart until the restorative force between them also balances the applied force. And so on down the line. In this way the force applied to one end of the string is transmitted without loss to the other end. The force transmitted by a string or other connector is called tension (Ft).
Describe weight
> direction of any vector representing weight (Fw) is downward toward the center of the earth
if body is drawn to scale, we show its weight by means of a vector placed on the vertical line through the center of gravity; that is, through the point of balance
a body resting on a sharp point does not fall if this point lies precisely underneath the center of gravity of the body
a body hanging on a cord attached to the center of gravity of the body does not rotate or swing
in both cases, the body acts as if all of its mass were concentrated at its center of gravity
Describe friction
> may be represented by a vector because friction is a force
vector’s magnitude depends on the normal force (Fn) applied to the surface and on the coefficient of the friction
vector’s direction is always opposite to motion
as long as a moving object remains in contact with a frictional surface or medium, the friction vector changes direction whenever the object changes direction
Describe translational equilibrium
> a body that is not accelerating is in translational equilibrium
if it is at rest, the body does not move
if it is moving, the body does not change direction or speed
translational equilibrium donly possible in the absence of a net force acting on a body (Sigma F = 0)
Define concurrent vectors
two or more vectors acting simultaneously upon the same point
Define resultant
a single vector representing the same effect as concurrent vectors acting separately
Define equilibrant
the force that achieves equilibrium directly opposite of the resultant
Describe how to find the equilibrant
> method of finding the equilibrant of 2 or more concurrent forces is quite simple: find their resultant and then reverse its direction
