Mechanics Flashcards
What is velocity?
The rate of change of displacement per unit time and it is represented by the gradient of a displacement-time graph
What is acceleration?
The rate of change of speed/velocity per unit time. It is represented by the gradient of a velocity-time graph
How is displacement represented on a graph?
The area under a velocity-time graph
Negative area shows an object returning to its starting point
What is a scalar?
A quantity with only magnitude
What is a vector?
A quantity with both magnitude and direction
Name the scalar quantities
- Mass
- Time
- Energy
- Temperature
- Length
- Speed
Name the vector quantities
- Displacement
- Force
- Velocity
- Acceleration
- Momentum
Why do projectiles follow a curved path?
Horizontal velocity remains constant but vertical velocity is affected by acceleration due to gravity. Horizontal and vertical components of the object’s motion are completely independent
Steps for projectile motion calculations
- Resolve the initial velocity into its horizontal and vertical components
- Use v cos θ for horizontal components
- Use v sin θ for vertical components
- Use the vertical component to work out how long the projectile is in the air
- Use the horizontal component to work out how far it goes while its in the air
How can projectile motion be investigated using a video camera?
- Set up a video camera with a known framerate in front of a metre ruler
- Record the position of a ball bearing (for example) in each frame after it is projected
- Use the distance travelled between frames to calculate the velocity
How can projectile motion be investigated using strobe photography?
- Set a camera to a long exposure in front of a reference object like a metre ruler or a screen with a grid
- A strobe light flashes repeatedly, which will light up the projectile at regular intervals so it appears at multiple times in the same photograph in a different position each time
- Work out how far the object travels between flashes of the strobe, and use the time between flashes to work calculate the velocity of the projectile between the flashes
> Horizontal distance between the objects remains constant, and the vertical distance between images is smallest at the top of the arc as the projectile slows down and changes direction
Velocity time graphs - acceleration
Acceleration is the gradient of a velocity time graph, and uniform acceleration is a straight line. The steeper the gradient, the greater the acceleration.
y = mx + c can be arranged into v = u + at, so a is gradient (m) and initial speed is the y intercept (c)
Acceleration time graphs
The height of the graph shows an object’s acceleration at a time and the area underneath it shows the object’s change in velocity. A negative gradient shows the object decelerating and if a = 0 then the object is moving with constant velocity
Free body force diagrams
They should show a single body on its own and should include all forces that act on a body, but not the forces it exerts on other objects. Arrow labels should show the size and direction of the forces, which will be balanced if the object is in equilibrium
Resolving forces
Separate the forces into 2 independent forces acting at right angles to each other which will not affect each other since they are perpendicular, then use trig to find the size of a component force in a particular direction.