Physical Science 1421
Department of Physics and Geology Linear Motion
Equipment Needed Qty Equipment Needed Qty
Photogate 2 Track 1
Dynamics Cart 1 Photogate Bracket 2
Five Pattern Picket Fence 1 Angle Indicator 1
Table Clamp 1 Metal Rod 1
Background
We are exposed to motion all the time, from the movement of the sun and moon to cars and people. The
simplest form of motion is in a straight line or linear motion. Speed is ‘how fast an object is moving’.
Acceleration is used to indicate a change (increase or decrease) in speed. An average speed can be a
useful value. It’s the ratio of the overall distance an object travels and the amount of time that the object
travels.
Distance
Average Speed = Time
If you know you will average 50 miles per hour on a 200 mile trip, it’s easy to predict how long the trip
will take. On the other hand, the highway patrol office following you doesn’t care about your average
speed over 200 miles. The patrol officer wants to know how fast you’re driving at the instant the radar
strikes your car, so he or she can determine whether or not to give you a ticket. The officer wants to
know your instantaneous speed.
If you measure average speed of a moving object over smaller and smaller intervals of distance, the
value of the average speed approaches the value of the object’s instantaneous speed. The motion of the
cart is due to gravity giving the cart almost constant acceleration when the friction between the track and
the cart is minimal. Assuming the initial speed of the cart is zero, we can also find the final speed and
the acceleration of the cart with simple algebra.
SpeedAverageSpeedFinal
×
=
2
2
2
Time
Distance
onAccelerati
×
=
Acceleration is defined as the time rate of change of speed.
SAFETY REMINDERS
• Follow all directions for using the equipment.
