4.1 Force, energy, and momentum Flashcards
Define scalar.
A quantity that only has magnitude.
Define vector.
A quantity with magnitude and direction.
Which of distance and displacement is a scalar and a vector?
- Distance is a scalar
- Displacement is a vector
Which of speed and velocity is a scalar and a vector?
- Speed is a scalar
- Velocity is a vector
Which of mass and weight is a scalar and a vector?
- Mass is a scalar
- Weight is a vector
Decompose this vector into x and y components
Define equilibrium.
For an object to be equilibrium, both the resultant force and resultant
moment acting on the object must be equal to zero.
Object either stationary or moving with constant velocity.
How can the forces acting on a object be shown to be in equilibrium with vector components?
- Horizontal components sum to zero
- Vertical components sum to zero
How can the forces acting on a object be shown to be in equilibrium with a scale diagram?
Draw a closed triangle.
Define a moment.
Product of the force and the perpendicular distance from the line of action of the force to the point.
(Moment=Fd)
Define a couple.
A pair of equal and opposite coplanar forces.
State the principle of moments.
Sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments for a system in equilibrium.
Define centre of mass.
The point through which all the mass of an objects acts.
Where is the centre of mass for a uniform object?
In the centre of the object.
Define displacement.
The overall disatance travelled from the starting point.
Define velocity.
Rate of change of displacement.
What is ‘instantaneous velocity?’
Velocity of an object at a specific point in time.
How is ‘instantaneous velocity’ found graphically?
Measuring the gradient of a tangent to a displacement-time grpah.
What is ‘average velocity?’
Velocity over a specific period of time.
How is ‘average velocity’ found?
Change in displacement divided by the change in time.
What does a straight (non-flat) line of a displacement-time graph show?
Constant speed.
What does a curved line of a displacement-time graph show?
Changing speed.
What is uniform acceleration?
Where velocity of object, moving along a straight line, changes at a constant rate.
Constant gradient on velocity-time graph
What is non-uniform acceleration?
Where the direction of motion of an object changes, or its speed changes at a varying rate.
Changing gradient on velocity-time graph
What is the graident of a displacement-time graph?
Velocity.
What is the graident of a velocity-time graph?
Acceleration.
What is the area of a velocity-time graph?
Displacement.
What is the area of an acceleration-time graph?
Change in velocity.
What do the letters in SUVAT represent?
S - displacement
U - initial velocity
V - final velocity
A - acceleration
T - time
How do the SUVAT equations reflect that that all objects fall at the same rate?
Mass is not included in the SUVAT equations, showing that the mass of an object does not affect its speed or acceleration.
What SUVAT would we use if we weren’t given S?
What SUVAT would we use if we weren’t given V?
What SUVAT would we use if we weren’t given A?
What SUVAT would we use if we weren’t given T?
Define free fall.
Where an object experiences an acceleration of g.
Define friction.
A force which opposes the motion of an object.
Define drag.
A (friction) force that opposes motion of an object in a fluid.
Define lift.
An upward force created on an object travelling through a fluid due to the object’s shape.
Define terminal velocity.
When frictional forces equal the driving forces, resulting in equilibrium (zero acceleration).
What is Newton’s 1st law?
An object will remain at rest of travelling with constant velocity, until a resultant force acts upon it.
What is Newton’s 2nd law?
Acceleration of an object is proportional to the resultant force acting on the object.
What do the letters represent in this equation?
What is another way to define Newton’s 2nd law?
The resultant force acting on an object is equal to the rate of change of momentum of the object.
What do the letters represent in this equation?
What is Newton’s 3rd law?
Every action has an equal and opposite reaction. If an object exerts a force on another object, then the other object must exert a force back, that is opposite in direction and equal in magnitude.
State conservation of (linear) momentum.
Total momentum before an event is equal to total momentum after the event.
Assuming no external forces are acting.
Define impulse.
Change in momentum.
What do the letters represent in this equation?
What is the area of a force-time graph?
Impulse
Define elsatic collision.
KE before an event is equal to KE after the event.
KE is conserved.
Define inealstic collision.
KE before an event is not equal to KE after the event.
There is a change in KE
What is ‘rate of doing work’ equal to?
Rate of energy transfer.
What do the letters represent in this equation?
Define work done.
Energy transferred by the component of the force in the direction the object is moving.
What do the letters represent in this equation?
What is the area of a force-displacement graph?
Work done
What is the equation for power in terms of force?
What do the letters represent in this equation?
Define efficiency.
State conservation of energy.
Energy cannot be created or destroyed, only transferred into other forms of energy.
What is the equation for KE?
What do the letters represent in this equation?
What is the equation for GPE?
What do the letters represent in this equation?
