P5 Forces - random revision (pages 201 - 216) Flashcards
Give two examples of quantities that have both magnitude and direction.
Any two from e.g.:
force
velocity
displacement
What property does a vector quantity have that a scalar quantity does not?
Direction
Speed and distance are both examples of what type of quantity?
Scalar
Define the term ‘non‑contact force’ and give one example of this type of force.
A force where objects do not need to be touching for the force to act. Any one from e.g.: magnetic force, electrostatic force, gravitational force.
Define ‘weight
The force acting on an object due to gravity.
What quantity is measured using a calibrated spring balance?
Weight
Give the equation that links mass, weight and gravitational field strength.
W=mg/ weight= mass ×gravitational field strength
How could you work out the resultant force created by two forces acting on an object in the same direction?
E.g. add them together
When work is done against friction to move an object, how would the object’s temperature change?
It would increase
State the equation linking the work done by a force with the force and the distance moved along the line of action of the force.
W=Fs/ Workdone= force ×distance(moved along the line of action of the force)
How much work is done when a force of 1newton causes an object to move 1metre?
1joule
Describe how to use a scale diagram to find the size of the resultant force acting on an object.
Draw all the forces acting on the object out ‘tip‑to‑tail’ and to scale. Then draw a straight line from the start of the first force to the end of the last force. This line is the resultant force. Measure the length of the line and use the scale chosen to find the size of the resultant force.
If all the forces acting on an object are drawn out ‘tip‑to‑tail’ in a scale diagram and form a closed shape, what is the size of the resultant force acting on the object?
Zero
Describe how to resolve a force that is acting at an angle into its horizontal and vertical components.
E.g. draw the force to scale on a scale grid at the correct angle and then add horizontal and vertical lines from each end of the force, so they make a right‑angled triangle. The horizontal and vertical components can then be measured and the size of each force determined using the scale of the grid.
Why does more than one force have to act on an object for it to deform?
If just one force acts on an object, it will only cause the object to move, not change its shape.
What type of deformation does an object undergo if it is stretched by forces and does not return to its original shape after the forces are removed?
Inelastic deformation
What does each letter represent in the equationF=ke?
Fis the force,kis the spring constant andeis the extension.
What is the name of the point where the relationship between the force applied to a spring and its extension stops being linear?
Limit of proportionality.
Doing work to stretch an object elastically causes energy to be transferred to which energy store?
Elastic potential energy store
For each of the following, state whether it is a scalar or vector quantity:
displacement
speed
velocity
distance
Displacement−vector
Speed−scalar
Velocity−vector
Distance−scalar
Give an example of a situation where an object is moving with a constant speed but with a velocity that is constantly changing.
E.g. travelling in a circle.
How do you calculate the average speed of a journey?
Divide the total distance travelled in the journey by the total time taken.
Give an estimate of an average walking speed and an average speed of a car inm/s.
Walking: e.g. about 1.5m/s.
Car: e.g. about 25m/s.
What is the typical speed of sound in air?
330 m/s
What are the units of acceleration?
m/s2
True or false? The equationv2−u2=2ascan be used to find the velocity of an object with a changing acceleration.
False. (The equation can only be used for an object with a constant acceleration.)
Describe how moving at a constant speed is represented on a distance‑time graph
A straight line with a positive/upwards gradient.
What does a horizontal line on a distance‑time graph for an object represent?
The object is stationary / not moving.
Describe how deceleration is represented on a distance‑time graph.
A curved line with its gradient getting shallower / levelling off over time.
What quantity is equal to the area under a section of a velocity‑time graph?
The distance travelled in that time period / section of the graph.
Define ‘terminal velocity’.
The maximum velocity a falling object can reach without any added driving forces. It’s the velocity at which the drag acting on the object matches its weight.
What is the resultant force acting on an object that is travelling at a terminal velocity?
0N / there is no resultant force.
What is Newton’s First Law for a stationary object?
If the resultant force acting on a stationary object is zero, it will remain stationary.
If the resultant force acting on a stationary object is zero, it will remain stationary.
False. A resultant force must act on an object to change its velocity.
According to Newton’s First Law, what can you say about the forces acting on an object if it is moving at a constant velocity?
They are balanced / there is no resultant force.
Describe, in words, the relationship between an object’s acceleration and the size of the resultant force acting on the object.
The acceleration of an object is directly proportional to the resultant force acting on it.
What does each letter represent in the equationF=ma?
Fis the resultant force acting on an object,mis the mass of the object andais the acceleration of the object.
What quantity is a measure of how difficult it is to change the velocity of an object?
Inertial mass.
State Newton’s Third Law
When two objects interact, they exert equal and opposite forces on each other.
True or false? In an investigation into the acceleration of a trolley, increasing the mass of the trolley, and keeping the force acting on it the same, will decrease the acceleration of the trolley. Explain your answer.
True. If the mass increases, the acceleration must decrease, because acceleration= force÷mass.
What is the difference between stopping distance and braking distance?
The stopping distance is the distance travelled between seeing a hazard and coming to a stop, rather than the distance travelled between applying the brakes and coming to a stop (braking distance).
Give two factors that affect thinking distance.
Speed.
Reaction time
Give one reason why a driver’s reaction time could be higher than normal, making their thinking distance longer.
Any one from e.g.:
They are tired.
They are under the influence of drugs/alcohol.
Explain how the quality of brakes can affect a vehicle’s stopping distance.
Worn or faulty brakes apply less force so take longer to stop the vehicle, and therefore increase the stopping distance.
Other than the quality of the brakes, what is one property of a vehicle that affects its braking distance?
E.g. the condition of its tyres.
Give two examples of poor road or weather conditions that can increase a car’s braking distance.
Any two from e.g.:
wet conditions
ice
leaves on the road
oil on the road
Describe the forces and energy transfers that occur when a car brakes.
The brakes provide a frictional force that transfers energy from the car’s kinetic energy store to the thermal energy stores of the brakes.
What are two potential dangers of a car experiencing a large deceleration due to braking?
Skidding.
Brakes overheating
What is the typical range in which a person’s reaction time would fall?
0.2 to 0.9seconds.
What does each symbol represent in the equationp=mv? State the units of each variable.
pis momentum inkgm/s,mis mass inkg,vis velocity inm/s.
State the principle of conservation of momentum
In a closed system, the total momentum before an event is the same as the total momentum after the event.
What is the momentum of a stationary object?
Zero. / It has no momentum
During an explosion, an object with no momentum can split into multiple pieces moving at high speeds. How is momentum conserved in this type of situation?
The pieces of the object move in different directions. Momentum is a vector quantity, so the overall momentum will still be zero because the momenta of each piece cancel out.
