Mechanics 1 Flashcards
Acceleration, momentum and weight are examples of what type of quantity?
Vector
Draw the vector diagram showing a stationary object on a flat desk
Weight acting down, equal and opposite reaction force acting up.
Draw the vector diagram showing an object on a flat desk moving at a constant speed.
Weight acting down, equal and opposite reaction force acting up, thrust force acting in direction of motion, equal but opposite force of friction acting against the force of motion.
Draw the vecor diagram showing a stationary object on an inclined plane (a slope).
Weight, resolved to act in vertical and horizontal planes (down the slope and at 90 degrees to down the slope), friction acting up the slope (equal but oposite to the component of weight acting down the slope, reaction force acting at 90 degrees to the slope, equal, but opposite magnitue to the component of weight acting at 90 degrees to the slope.
Draw the vector diagram showing an object on an inclined plane moving at a constant speed.
Weight, resolved to act in vertical and horizontal planes (down the slope and at 90 degrees to down the slope), friction acting up the slope (equal but oposite to the component of weight acting down the slope, reaction force acting at 90 degrees to the slope, equal, but opposite magnitue to the component of weight acting at 90 degrees to the slope.
What is a vector quantity?
A quantity with both magnitude and direction
What is a scalar quantity?
A quantity with only a magnitude associated with it
What is the sum of two or more vectors called?
Resultant
Give three examples of scalar quantities
Any three from speed, distance, pressure, temperature, mass, density, power
Give three examples of vector quantities
Acceleration, velocity, displacement, Force, Weight, momentum
State the forces that will act on a helicopter that is moving horizontally
Lift, Air resistance, Weight, Thrust
How can drawn force vectors be arranged to show that an object has constant velocity?
Closed triangle of vectors. This shows the forces are in equilibrium.
What is the difference between a vector quantity and a scalar quantity?
Vector has a direction, scalar does not.
A value with magnitude only is a ________?
Scalar
A value with magnitude and direction is a ____________?
Vector
Distance an speed are examples of _________ quantities
scalar
What is the name given to a vector formed by adding vectors together?
Resultant vector
Force, displacement and velocity are examples of __________ quantities
Vector
What is a contact force?
A force between two object which are touching
What is a non-contact force?
A force between objects which are separated by space.
Give two examples of contact forces
e.g. friction, air resistance, tension, drag, reaction
List three non-contact forces
gravitational, electrostatic, magnetic
The single force which has the same effect as the combination of all the different forces acting on an object is the ______________ _______________.
resultant force
If a body is in equilibrium, what’s the sum of all the forces acting on it?
0
Explain what equlibrium means in the context of a moving object.
Equilibrium means that the moving object will have no resultant force acting on it so it will be moving at a constant speed.
Define weight
The force of gravity acting on an object’s mass
Give the formula which links Weight, mass and gravitational field strength
W = mg
What is the value of g on earth?
9.81 ms-2
What is a moment?
A moment is the turning effect of a force around a turning point
How do you calculate a moment?
moment = F x d
What name is given to a pair of forces of equal size which act perpendicular to each other in opposite directions?
A couple
How can you calculate the centre of mass of an irregularly shaped object?
Hang it from a point, draw a line down, do this 3 times, the point where the three lines meet will be the COM.
How can you use the principle of moments to calculate the mass of a beam?
Hang the beam from a point (not it’s COM) and hang masses from the beam, taking moments around one side will allow you to calulate the moments around the COM.
What is the name of the single point at which an object’s mass appears to act?
centre of mass
The centre of mass of an object is…
the single point at which the objects weight appears to act.
What unit are moments measured in?
N m
What is meant by centre of gravity?
The point in a body where the weight of the object appears to act
Define the moment of a force
Product of the force and the perpendicular distance between the line of action of the force and the turning point
State the principle of moments
The principle of moments states that for a system in equilibrium, the sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point.
For a uniform regular solid, where will its centre of mass be?
The centre of the object
Define a couple
A couple is a pair of forces of equal size which act parallel to each other, but in opposite directions.
What affect will a couple have on an object?
It will cause the object to rotate
Which of the following statements regarding equilibrium is true?
A) A body in equilibrium has no forces acting on it.
B) A body moving with constant velocity is in equilibrium. C) A body in freefall is in equlibrium.
D) A body in equilibrium will always be at rest.
B) A body moving with constant velocity is in equilibrium.
Explain why a wine glass containing wine is less stable than an empty one.
The center of mass is lower on an empty wine glass, so will be more stable, than a full one.
How can an object be made more stable?
Widen the base of the object or lower the centre of mass
If the centre of mass of a beam is directly over a pivot, how will the beam move?
The beam will remain stationary as there is no resultant moment.
In order to calculate which direction a see saw will rotate in, what do you need to calculate?
The clockwise and anticlockwise moments around the pivot.
State and explain a feature of a crane that helps prevent it from falling over when lifting heavy things
A counterweight provides a sufficiently large moment in the opposite direction. They also have wide heavy bases.
What is meant by speed?
How fast something is moving, regardless of direction
What is meant by displacement ?
How far an object has travelled form its start point in a given direction.
What is the definition of velocity?
The rate of change of displacement (speed in a given direction)
What is the definition of acceleration?
The rate of change of velocity.
In the SUVAT equations, what does s represent?
Displacement (m)
In the SUVAT equations, what does u represent?
Initial velocity (ms-1)
In the SUVAT equations, what does v represent?
Final velocity (ms-1)
In the SUVAT equations, what does a represent?
Acceleration (ms-2)
In the SUVAT equations, what doest represent?
Time (s)
Under what conditions can the SUVAT equations be used?
Constant acceleration
What does free fall mean?
Only force acting is gravity
If an object is dropped. What is its initial velocity, u?
0
If an object comes to rest. What is its final velocity, v?
0
When a ball is thrown upwards, what is its velocity at its highest point?
0 ms-1
When a ball is thrown upwards, what is its acceleration on the way down?
g (9.81m s-2)
When a ball is thrown upwards, what is its acceleration on the way up?
g (9.81m s-2)
What does the gradient of a displacement-time graph tell you?
The velocity of the object
How would a stationary object be represented on a displacement-time graph?
Straight line with 0 gradient
On a displacement-time graph a straight, diagonal line represents…
constant velocity
On a displacement-time graph a steeper gradient represents…
Larger velocity
On a displacement-time graph a shallower gradient represents….
Smaller velocity
On a displacement-time graph an upward curve represents…
acceleration
On a displacement-time graph a curved line becoming horizontal represents…
decelleration
On a displacement-time graph a horizontal line represents…
A stationary object
On a displacement-time graph the gradient is used to calculate the …
Velocity
On a curved displacement-time graph showing an accelerating object, how can you calculate instantaneous velocity?
Draw a tangent and find the gradient at that point
On a velocity time graph an upwards, diagonal straight line represents …
Constant acceleration
On a velocity - time graph a steeper gradient represents?
Greater acceleration
On a velocity - time graph a shallower gradient represents?
Smaller acceleration
On a velocity time graph a downwards, diagonal straight line represents …
decelleration
On a velocity time graph a horizontal line represents …
Constant velocity
On a velocity time graph a horizontal line along the x-axis represents…
stationary object
On a velocity time graph, when the line falls below the x-axis it indicates that the object is …
moving backwards
Calcuating the gradient of a velocity time graph gives the …
acceleration
Calculating the area under a velocity time graph gives the …
Displacement of the object
On a velocity - time graph for a ball being dropped and rebounding. What will the gradient of the line be?
g (9.81m s-2)
On an acceleration - time graph what does a straight line at acceleration = 0 mean?
The object is moving at a constant velocity
On and acceleration - time graph what does a positive gradient mean?
The rate of acceleration is increasing.
On and acceleration - time graph what does a negative gradient mean?
The rate of acceleration is decreasing (above the x-axis).
The rate of decelleration is increasing (below the x-axis)
On and acceleration - time graph what does the area under the graph tell you ?
The change in velocity
How would you find the velocity from an acceleration - time graph?
The area under the graph gives you the velocity
What does negative acceleration on an acceleration - time graph show?
Decelleration
How would constant velocity appear on an acceleration - time graph?
Straight, horizontal line along through 0 on the vertical axis.
True or false? An object with a resultant force of 0 N acting on it must be at rest.
False. An object that’s moving at a constant velocity will also have a resultant force acting on it.
Three coplanar forces are acting on an object. Describe how you could use a scale drawing to show whether or not the object is in equilibrium.
Using a scale drawing. Draw the forces tip to tail. If they form a closed triangle, then the object is in equilibrium.
True or false? An object suspended from a string will always hang so that its centre of mass is vertically in line with the string.
True.
A student travels into space in a spaceship with a mass of 2.03 x 106 kg. When it lands on an unknown planet, the weight of the spaceship is 1.75 x 107 N. Determine the gravitational field strength on the unknown planet?
8.62 Nkg-1
True of false? An object is in free fall if the only force acting on it is air resistance.
False
True or false? An object undergoing projectile motion is accelerating in both the horizontal and vertical directions.
False
An object is travelling at v ms-1 at an angle of ø above the horizontal. What equation should be used to determine the horizontal component of its velocity?
vcosø
True or false? The faster an object is moving through air, the lower the air resistance acting on it.
False. The faster an object moves through air, the greater the air resistance acting on it.
