P5 - FORCES Flashcards
What is a contact force?
When objects physically touch.
E.g, friction, air resistance and tension.
What is a non-contact force?
When objects are not touching.
E.g, magnetism, electrostatic force and gravity
What is a scalar quantity?
A quantity that only has magnitude
What is a vector quantity?
A quantity that has magnitude and direction
How do we find the resultant vector?
Adding the two numbers together on a diagram.
If at right angles = Pythagoras is used or trigonometry.
What does it mean if there’s no resultant force?
No resultant force = no acceleration.
Name some similar scalar and vector quantities
Distance (Scalar), Displacement (Vector)
Speed (Scalar), Velocity (Vector)
What is WEIGHT?
Weight is the force that gravity pulls an object down with.
What is the equation for weight?
Weight = mass x gravitational field strength #
W=mg
UNITS; weight (N), mass (kg), gfs (N/kg)
What is WORK DONE?
‘energy transferred by a force’.
What is the equation for work done?
work done = force x distance
W=fd
UNITS; work done (J), Force (N), Distance (M)
What is HOOKE’S LAW?
Force and extension and directly proportional.
>Any objects that deforms elastically obeys this law.
What is the equation for force?
Force = spring constant x extension
F=ke
UNITS; force (N), spring constant (N/m), extension (m)
Describe the practical for Hooke’s law
-Secure a clamp to a bench using a G-clamp.
-Use bosses to attach two clamps to the clamp stand.
-Attach the spring to the top clamp, and a ruler to the bottom clamp.
-Adjust the ruler so that it is vertical, and with its zero level with the top of the spring.
-Hang a 100g slotted mass carrier from the spring. Measure and record the new length of the spring.
-Add a 100g slotted mass to the carrier. Measure and record new length of the spring.
-Repeat step 7 until a total of 1000g has been added.
Newton’s Equations Of Motion
SUVAT
S- displacement (m)
U- initial velocity (m/s)
V- final velocity (m/s)
A- acceleration (m/s^2)
T- time (s)
What is the initial velocity if something is at rest + final velocity if something stops?
If starting at rest, u=0m/s
If stopping, v=0m/s
What is Newton’s 1st law?
No resultant force acts on an object, its motion will be constant (velocity will not change).
What is Newton’s 2nd law?
F=ma (force = mass x acceleration)
Describe the practical for investigating the effect of force on acceleration
-Use the metre ruler to measure out intervals on the bench. Draw straight lines with pencil or chalk across the table at these intervals.
-Attach the bench pulley to the end of the bench.
-Tie some string to the trolley. Pass the string over the pulley and attach the mass hanger to the other end of the string.
-Make sure the string is horizontal and is line with the trolley.
-Hold the trolley at the starting point.
-Attach the full set of weights to the end of the string.
-Release the trolley at the same time as the stopwatch is pressed. (Lap mode at each measured interval on the bench). Final time is at 1.0m.
-Record the results in a table and repeat step 7 to calculate an average time for each interval.
-Repeat steps 5-8 for decreasing weights on the weight hanger.
What is Newton’s 3rd law?
For every action (force), there is an equal and opposite reaction (force).
How do you work out the stopping distance of a car?
Thinking distance + braking distance
What can thinking distance be affected by?
-speed
-distractions
-drugs
-alcohol
-tiredness
What can braking distance be affected by?
-condition of brakes/tyres
-road conditions#
-weather conditions
What is the equation for momentum?
momentum = mass x velocity
m=mv
UNITS; momentum (kgm/s), mass (kg), velocity (m/s)
What happens to momentum during a collision?
In any collision, total momentum is ALWAYS conserved.
rebound: m1u1 = m1u1 + m2u2 (if there’s a second object)
coupling: m1u1 = mv
recoil: 0 = m1v1 + m2v2
