Mechanics Flashcards
What must always be true when using the SUVAT equations of motion?
The acceleration must be uniform- if the acceleration is changing, the equations are not valid
What does the gradient of a Distance-time graph represent?
Speed
What does the gradient of a displacement- time graph represent?
Velocity
What does the gradient of a velocity-time graph represent?
Acceleration
Describe the shape of a velocity-time graph for an object travelling with uniform acceleration
If acceleration is constant, the gradient of the velocity-time graph will be constant and so it will from a straight line graph
Describe the shape of a velocity-time graph for an object travelling with non-uniform acceleration.
If acceleration is not constant, the gradient of the velocity-time graph will change and so it will form a curve
Compare the velocity-time graphs for a uniformly accelerating and a uniformly decelerating object.
- For an accelerating object, the gradient will be positive
- For a decelerating object, the gradient will be negative
What is a scalar quantity?
A scalar quantity is one that has a magnitude but not a fixed direction
What is a vector quantity?
A vector quantity is one that has a magnitude and a fixed direction
Give five examples of scalar quantities.
- Distance
- Speed
- Mass
- Energy
- Temperature
Give five examples of vector quantities.
- Displacement
- Velocity
- Acceleration
- Momentum
- Force
How is a vector quantity represented on a diagram?
- As an arrow
- The direction of the arrow represents the direction of the quantity
- The length of the arrow represents the magnitude of the quantity
What does resolving a vector involve?
Splitting the vector into two perpendicular components
Define the horizontal component of a vector at an angle to the horizontal in terms of V and theta.
horizontal component: X = V cos theta
Define the vertical component of a vector at an angle to the horizontal in terms of V and theta.
Vertical component: y = V sin Theta
Describe the relationship between the perpendicular components of a vector.
The perpendicular components are independent of each other.
How should the components of a projectile be handled when carrying out calculations? (2)
- The horizontal and vertical components are independent of each other and so should be treated separately
- SUVAT should be used separately for each component
If a projectile is moving freely under gravity, what can be said about the vertical acceleration?
The vertical acceleration will be the acceleration due to gravity and so will have a magnitude of 9.81 ms {-1}
State Newton’s first law of motion in words.
An object at rest will remain at rest, and an object moving with a given velocity will continue moving with that same velocity, unless acted on by an external resultant force
State Newton’s second law of motion in words.
The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass
State the defining equation of Newton’s second law of motion.
Resultant Force (N) = Mass(kg) x Acceleration (ms{-2}
Can an object travelling with constant speed change direction, without an external force acting?
-For an object to change direction, its velocity must change.
- This means there must be an acceleration
- An acceleration cannot occur without an external resultant force acting
Describe the forces acting on an object travelling at terminal velocity.
- The forces are balanced in both the vertical and horizontal components of its motion
- There is no resultant force and therefore no acceleration
What is meant by terminal velocity?
-For a given set of conditions, the terminal velocity is the maximum speed of the object.
- An object has zero acceleration at terminal velocity
