Physics Forces Nov 2018 Flashcards
What are the average speeds you need to know?
Walking = 1.0 - 2.0 m/s Jogging = 3.0 - 5.0 m/s Cycling = 6.0 - 8.0 m/s Car on local road = 10.0 - 15.0 m/s Car on motorway = 25.0 - 30.0 m/s Plane flying = 200.0 m/s
What is the equation for average speed?
v = s/t speed = distanced travelled / time
How do you calculate speed from a distance - time graph?
Calculate the gradient of the line
How do you calculate speed from a distance - time graph when there is a curve
Draw a tangent at two points of the curve. Calculate the gradients of these tangents and then find an average speed.
What is the formula for acceleration?
a = (v - u)/t acceleration = (final velocity - initial velocity)/time
How can you tell if the object is accelerating or decelerating from numbers?
+ number = accelerating
- number = decelerating
How can you calculate the distance travelled from a velocity time graph?
Calculate the area underneath the graph
How can you calculate the distance travelled from a velocity time graph if it has an irregular shape? (Very unlikely in an exam)
Count all the whole squares under the graph and estimate the incomplete squares. Add together to get a total
What is the equation for acceleration when it is linked with displacement?
v2 - u2 = 2as
final velocity squared - initial velocity squared = 2 x acceleration x displacement
What is Newton’s 1st law?
An object will stay stationary or at a constant speed unless acted upon by an unbalanced/resultant force
What is Newton’s 2nd law?
When an unbalanced force acts upon an object it accelerates. The object can accelerate, decelerate or change direction. A larger force creates a larger acceleration and a larger mass is harder to accelerate
What is Newton’s 3rd law?
For every action there is an equal and opposite reaction. In every interaction there is a pair of forces acting on two objects. The size of the force on the first object equals the force on the second. The direction of force on the first object is opposite to the direction of force on the second.
What is the equation for Newton’s 2nd law?
f = ma Force = mass x acceleration
What is the equation for stopping distance?
Stopping distance = thinking distance + braking distance
What factors can affect thinking distance?
Tiredness, alcohol, drugs, distractions (e.g. phones) & speed travelling at
What factors can affect braking distance?
Quality of road, weather conditions, car conditions, mass of car, force exerted on the pedal & speed travelling at
What is the equation for braking distance and change in kinetic energy?
Fs = 1/2mv2
work done = change in kinetic energy
What is the equation for momentum?
p = mv Momentum = mass x velocity
What must you do with momentum for two objects coming together?
Have a +/- direction
What is the equation for force with change of momentum?
is f = ma we can substitute a for (v-u)/t. This makes
f = m(v-u)/t. (mv-mu = change in momentum)
What is the definition of a scalar?
A quantity with only magnitude (size) and no direction
What is the definition of a vector?
A quantity with magnitude (size) and direction
What is velocity?
A speed in a defined direction
What is displacement?
A distance travelled in a defined direction
What is a force?
A push or a pull
What are the two types of forces? Definitions?
Contact Force - a force between two objects when they touch
Non-contact Force - a force between two objects that are physically separated
What is the unit for forces?
N - Newtons
What is the equation for weight?
W = mg Weight = mass x gravitational field strength
What is the centre of mass?
The point through which the weight of an object can be taken to act
What is the resultant force?
A single force that has the same affect as all the forces together
How do you work out the resultant force?
Biggest number - smallest number = resultant force in direction of bigger number
What is momentum?
The product of mass and velocity
