What can you say about the forces acting on a stationary object or an object travelling at a constant speed?
They are equal and opposite
What is the unit of force?
The Newton (N)
What is the 'resultant force'?
A number of forces acting on an object that are replaced by a single force that has the same effect as the original forces acting together.
What happens if the resultant force is zero?
The object remains stationary if it was at rest
Continues to move at the same speed in the same direction if it was already moving.
What is the equation for resultant force?
Resultant force = mass x acceleration
(newtons,N) (kg) (m/s squared)
What happens if the resultant force is in the same direction as the velocity?
The velocity of the object increases. This is positive acceleration.
What happens if the resultant force is opposite to the direction of the velocity?
The velocity of the object decreases and we call this negative acceleration (or decceleration)
Name three factors that increase thinking distance.
All of these increase reaction times
Name three factors that increase braking distance.
- The speed the vehicle is travelling - faster = bigger braking distance
- The road/ weather conditions - icy or wet roads mean the driver has to break with less force to avoid skidding therefore increasing braking distance
- Contition of the vehicle - eg. worn tyre treads reduce friction - increase braking distance.
What is the equation for stopping distance?
Stopping distance = thinking distance + braking distance
What is the difference between mass and weight?
Weight = The force of gravity on an object and is measured in Newtons (N)
Mass = The quantity of matter in an object and is measured in grams/kilograms (g/kg)
What is gravitational field strength and what is it measured in?
Gravitational field strength is the force of gravity on a 1kg object at the place the object is. The unit of gravitational field strength is the newton per kilogram (N/kg)
What is the equation for weight?
Weight = mass x gravitational field strength
(newtons,N) (kilograms,kg) x(newtons/kilogram,N/kg)
Explain terminal velocity, saying what it is and refering to graph shapes.
Terminal Velocity is when an object reaches a constant velocity as the drag force is equal and opposite to its weight. At terminal velocity, both the resultant force and acceleration are zero. On a graph you can tell when an object has reached terminal velocity because it flattens out.
What value (approximately) is the Earth's gravitational field strength at its surface?
If an object falls freely, what (approximately) is its acceleration?
Acceleration = resultant force/mass
= 10N (force of gravity) / 1kg
= 10m/s squared
Does the acceleration of an object increase or decrease as it falls through a fluid, and why?
Decreases, because the drag force increases and consequently the resultant force on it decreases.