Motion and Forces Revision Cards Flashcards
What is a vector quantity?
A vector quanitity is a quantity that has both DIRECTION and MAGNITUDE
What is the difference between mass and weight?
Mass is a scalar quantity, measured in kg and is the amount of matter in an object. Weight is a vector quantity, measured in N and is the force due to gravity on an object with mass.
Define displacement
Displacement is the distance travelled in a straight line, in a given direction.
Define velocity
Velocity is the speed in a particular direction.
What is the equation that links speed, distance and time?
Speed (m/s) = distance (m) / time (s)
What does the gradient of a distance time graph tell you?
Speed
What does the gradient of a displacement time graph tell you?
Velocity
What does a horizontal line on a displacement time graph tell you about the motion?
It is stationary
What do the letters stand for in the equation a=(v-u)/t?
a = acceleration in m/s2
v = final velocity in m/s
u = initial velocity in m/s
t = time in s
What is the acceleration due to gravity on Earth (g)?
g = 9.8m/s2
(This is often rounded to 10 in calculations)
What does the gradient of a velocity time graph tell you?
Acceleration
How do you calculate distance travelled from a velocity time graph?
Find the area under the line (you may need to break it into rectangles & triangles and add them together to find the total)
A car is driving around a roundabout at 20km/h. It is said to be accelerating - why?
Speed isn’t changing, but velocity is changing because DIRECTION is changing. A Change in velocity is an acceleration.
Which of Newton’s laws is this? “A moving object will continue to move at the same speed and direction unless an external force acts on it. A stationary object will remain at rest unless an external force acts on it.”
Newton’s FIRST law.
What is a centripetal force?
A ‘centre-seeking’ force. A force that acts towards the centre of a circle. There is always a centripetal force if something is moving in a circle.
What is the equation that links weight, mass and gravitational field strength? (Don’t forget units!)
Weight (N) = mass (kg) x gravitational field strength (N/kg)
Why does a sky diver accelerate when he first jumps out of the plane?
There is a resultant force acting downwards, as his weight is much larger than the air resistance while he is moving slowly.
Why does a sky diver stop accelerating some time after he jumps out of the plane?
As he speeds up air resistance increases. Eventually it gets so big in balances his weight. There is no resultant force, so no acceleration.
What is the equation usually linked with Newton’s second law?
F = m a
where
F = resultant force (N)
m = mass (kg)
a = acceleration in the direction of the force (m/s2)
Define inertial mass
Force(N) / Acceleration (m/s2)
How difficult it is to change the velocity of an object
Which of Newton’s laws is this? “If object A exerts a force on object B, object B exerts an equal but opposite force on object A”.
Newton’s THIRD law.
Action - reaction pairs act on _ _ _ _ _ _ _ _ _ objects.
Different
What is the equation for momentum? (Don’t forget units!)
Momentum (kg m/s) = mass (kg) x velocity (m/s)
p = m v
What is the equation that relates rate of change of momentum with force?
F = (mv - mu)/t
How can you reduce the force felt in a collision?
Increase the time taken to reduce the momentum to zero.
(F = (mv - mu)/t)
What is conservation of momentum?
The total momentum before a collision/explosion = the total momentum after the collision/explosion
What is the equation for stopping distance?
Stopping distance (m) = thinking distance (m) + braking distance (m)
What factors affect thinking distance?
those that affect reaction time, e.g. use of drugs/alcohol/caffeine, tiredness, distractions
AND
the speed of the car
What factors affect braking distance?
those that affect the car itself, e.g. quality of the tyres/road surface/brakes, the weather conditions
AND
the speed of the car
What is the purpose of a crumple zone?
To extend the TIME taken to bring the car to a halt, thus reducing the force felt by the passengers.
F = (mv - mu)/t
Other than a crumple zone, which safety feature of a car works by increasing the time taken for the driver of a car to come to a stop?
Air bag
