CPACS Flashcards
CPAC 1 Method
Suspend metre ruler vertically
Attach light gate at 0m and attach light gate at 0.1m
Configure lightgates and data logger to record time between
Drop card with mass attached from first light gate and allow to fall through second light gate
Record time and distance between light gates
Repeat for displacements up to 0.9m
CPAC 1 Physics Theory
Acceleration due to gravity is approximately constant earth and is detonated by constant, g
You can measure the time for the ball to travel a displacement.
The initial velocity, u, will always be 0.
s = ut + 1/2at^2 => s = 1/2at^2
CPAC 1 Graphical Analysis
Plot a graph of s (y-axis) against t^2 (axis) therefore the gradient is 1/2a where a is acceleration due to gravity
CPAC 1 Risk Assessment
Tripping - place bags under table
Place metre ruler on top of books to prevent ball from falling onto people’s toes or rolling
Apparatus - might topple over - place on centre of table
CPAC 1 Sources of Uncertainty
- Reading metre ruler - parallax
* Card length doesn’t match light gate configuration
CPAC 10 Method
- Measure the mass and the diameter of the
spheres. - Start a collision between a moving sphere and a
stationary one. Set the table or drawing board at a
slight angle and roll the sphere along the upper
edge of a rule. The collision occurs along the rule.
This enables you to familiarise yourself with the
equipment and allows for calibration. - After sufficient rehearsal, set up the digital camera
to record the collisions. Lay the surface out
horizontally and roll one sphere into a second
stationary one again. This time the collision is
unlikely to remain in one dimension, and there will
be three tracks to record. - Repeat, varying the line of approach so that a
variety of collision angles are employed. It may
help to mark the graph paper or dressmaking
paper where the stationary sphere is placed to
allow for small variations in approach. With
practice, you will be able to use spheres of
different diameters. - Use Tracker to analyse the video clips. Download
the video file from the camera to the computer that
runs Tracker and then load the clip into the
program. - Use the ‘velocity overlay’ feature so that the
software can analyse velocities. You will need to
multiply by the mass if you are to analyse the
momentum. - You will need to keep a record of your work. This
can either be on a digital file or by drawing the
diagrams on paper and annotating them clearly
and correctly.
CPAC 10 Graphical Analysis
It is probably easiest to lay the x-axis along the path of the incoming sphere, then the
components in the x-direction and the y-direction are the maximum and zero respectively.
2. You will need to measure velocities as vectors, having magnitude and direction, so measuring
angles is extremely important.
3. You should analyse the tracks to see if momentum is conserved along the line of the approach
and perpendicular to that line.
4. Construct a momentum vector triangle and use it to see if it closes (meaning momentum is
conserved). You can also use the vector triangle to consider energy. You should find that when
kinetic energy is conserved there is a right angle between the two spheres after collision (so
long as the target sphere was stationary and the spheres have the same mass).
CPAC 10 Physics Theory
p = mv
conservation of momentum
CPAC 10 Risk Assessment
Keep fingers out of way of spheres
Make sure spheres are contained on table
CPAC 10 Sources of Uncertainty
Measurement of mass
Measurement of velocity - use slow motion camera
Air resistance/friction
