P10: Forces and Motion Flashcards
What is the equation linking the resultant force, mass and acceleration?
Resultant Force = Mass x Acceleration
What is Newton’s 2nd Law?
F=ma, Acceleration of an object is directly proportional to the resultant force and inversely proportional to its mass.
What is inertia?
The tendency of an object to stay at rest or continue to move at a constant velocity.
Inertial mass is a measure of difficulty changing object’s velocity.
Why might the velocity of an object decrease?
If the resultant force is in the opposite direction to its velocity so it decelerates. Increases if in the same direction.
Describe method to find acceleration of a trolley.
- Set up by clamping a pulley onto the edge of a desk, attaching a string to the trolley and place the string over the pulley and attach the mass holder to the string.
- Place mass on mass holder and use W=mg to calculate the force.
- Measure the distance between the starting and finishing points of the trolley.
- Time how long it takes to travel or use light gate to determine speed and computer calculates acceleration. Use acceleration equation.
- Repeat for different masses and plot the force in the x axis and the acceleration in the y axis.
What is the difference between weight and mass?
• The weight of an object is the force acting on it due to gravity, measured in newtons.
• The mass of an object depends on the quantity of matter in it, measured in kilograms.
What is the equation for weight?
Weight (N) = Mass (kg) x Gravitational Field Strength (N/kg)
What is the terminal velocity of an object?
The terminal velocity of an object is the velocity it eventually reaches when falling and the weight of the object is equal to the frictional force on it, so the resultant force is zero. Weight = Air Resistance
What is the braking force?
The braking force of an object is the force needed for a vehicle to stop and it depends on its speed and mass. Friction and air resistance oppose the force. The greater the speed, the greater the deceleration so the braking force must be greater.
What is the stopping distance?
The shortest distance a vehicle can safely stop in. Depends on the speed and mass.
Stopping distance = Thinking distance + Braking distance
What is the thinking distance and how is it affected?
It is the distance travelled by a vehicle in the time it takes the driver to react.
Affected by tiredness, alcohol and drugs that increase/decrease reaction time and if there are any distractions.
What is the braking distance and what affects it?
The distance travelled during time the braking force acts.
Icy/wet roads or worn out brakes/tyres increase it.
What is the equation for momentum of a moving object?
Momentum (kg m/s) = Mass x Velocity
What is the law of conservation of momentum?
The total momentum before is equal to the total momentum after an event in closed systems where no external forces act.
This means when two vehicles collide, they exert equal and opposite forces and the total momentum is unchanged.
What are some ways to reduce impact forces?
• The longer the impact time, the more the impact force is reduced so momentum is also reduced:
- Cycle helmets and cushioned surfaces reduce impact forces by increasing impact times.
- Seat belts and air bags spread force across chest and increase impact time.
- Crumple zones give way in impact so increase impact times.
