A large crate filled with physics laboratory equipment must be moved up an incline onto a truck.
1. The crate is at rest on the incline. What can you say about the force of friction acting on the crate?
2.A physicist attempts to push the crate up the incline. The physicist senses that if he applies slightly more force the crate will move up the incline but cannot muster enough strength to get the motion started. What can you say now about the force of friction acting on the crate?
3. The first physicist gets a second physicist to help. They both push on the crate, parallel to the surface of the incline, and it moves at constant speed up the incline. How does the force exerted by the two physicists on the crate compare with the force of friction on the crate?
1. When the crate is at rest on the incline, the force of friction acting on the crate must be equal in magnitude but opposite in direction to the force pulling the crate down the incline due to gravity. This is known as the static friction.
To determine the force of friction, you can use the formula: Ffriction = μs * Fn
Where:
- Ffriction is the force of friction
- μs is the coefficient of static friction
- Fn is the normal force exerted on the crate (equal to the weight of the crate)
Note that the static friction force prevents the crate from sliding down the incline when it is at rest.
2. If the physicist cannot muster enough strength to get the motion started, it means that the force of friction acting on the crate is greater than the force the physicist is applying. In other words, the static friction force is larger than the force applied by the physicist.
3. When the two physicists push on the crate and it moves at a constant speed up the incline, it means that the force they exert is equal to the force of friction. This situation is known as dynamic or kinetic friction.
To determine the force exerted by the two physicists on the crate, you can calculate the sum of the forces exerted by each physicist. The force of friction, in this case, is equal to the sum of the forces applied by the physicists.
It's worth noting that the force of friction can be determined using the formula: Ffriction = μk * Fn
Where:
- Ffriction is the force of friction
- μk is the coefficient of kinetic friction
- Fn is the normal force exerted on the crate (equal to the weight of the crate)
By comparing the forces exerted by the physicists with the force of friction, you can determine whether the crate will move up the incline, remain at rest, or move at a constant speed.