Chapter 4, Forces Flashcards Preview

Physics: Forces and Motion > Chapter 4, Forces > Flashcards

Flashcards in Chapter 4, Forces Deck (24)
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1
Q

Defining equation for force?

A

F=ma (force=mass*acceleration).

2
Q

Unit for force?

A

Newtons.

3
Q

Difference between mass and weight?

A

Mass (measured in kg) is how much stuff there is, weight (measured in N) is the product of mass and g and gives the force applied to an object towards the centre of mass of the object it is in the gravitational field of.

4
Q

What is the centre of mass?

A

The point in an object through which weight acts, also if a force is applied through the centre of mass there is no net moment.

5
Q

How do you find the centre of mass of an object?

A

if you hang an object from a point you know the line through the point which is perpendicular to the earth goes through the centre of mass. You can use a plumb-line to help measure this position.

6
Q

What is weight?

A

The gravitational force acting through the centre of mass of an object.

7
Q

What is friction?

A

The resistive force from two rough objects rubbing against each other.

8
Q

What is drag?

A

The resistive force acting on an object travelling through a fluid.

9
Q

What is tension?

A

The force within a stretched object (usually string/rope)

10
Q

What is upthrust?

A

An upwards force acting on an object inside a fluid caused by the displacement of this fluid.

11
Q

What is the normal contact force?

A

The force acting 90 degrees to the surface an object is resting on stopping it falling through the object.

12
Q

On a smooth slope with an object resting on it what is the value of the normal contact force and the component of the weight down the slope?

A

Normal contact = component of weight perpendicular to slope = mgcos(theta), component of weight down slope = mgsin(theta).

13
Q

What are the main factors that is drag proportional to?

A

Speed of the object and cross sectional area, also shape of object, roughness/texture of object and the density and viscosity of the fluid.

14
Q

What is terminal velocity?

A

The point of equilibrium between weight and the drag force such that the net force is 0.

15
Q

What is the equation for the moment of a force?

A

moment = force * perpendicular distance.

16
Q

Unit for moments?

A

Newton meters.

17
Q

What is the principle of moments?

A

For a body in rotational equilibrium the sum of the anticlockwise moments about a point is equal to the sum of the clockwise moments about that same point.

18
Q

What is a couple?

A

Two equal forces acting in opposite directions about a point such that it rotates without having any displacement.

19
Q

What is the defining equation for density?

A

ρ = m/V (density = mass/volume).

20
Q

What is the defining equation for pressure?

A

p = F/A (pressure = force/area).

21
Q

What is the unit for pressure?

A

The Pascal (Pa).

22
Q

What does the equation p=hρg show?

A

pressure = height fluid column * density of liquid * acceleration due to gravity.

23
Q

What is the equation for upthrust?

A

upthrust = Axρg where A is the area on top, x is the height of the submerged object, ρ is pressure and g is acceleration due to gravity.

24
Q

What is Archimedes principle?

A

The upthrust exerted on a body in a fluid is equal to the weight of the fluid that body displaces.